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  • 1. Bailey, W. E.
    et al.
    Cheng, C.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Auffret, S.
    Zohar, S.
    Keavney, D.
    Warnicke, P.
    Lee, J. -S
    Arena, D. A.
    Detection of microwave phase variation in nanometre-scale magnetic heterostructures2013In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, p. 2025-Article in journal (Refereed)
    Abstract [en]

    The internal phase profile of electromagnetic radiation determines many functional properties of metal, oxide or semiconductor heterostructures. In magnetic heterostructures, emerging spin electronic phenomena depend strongly upon the phase profile of the magnetic field (H) over tilde at gigahertz frequencies. Here we demonstrate nanometre-scale, layer-resolved detection of electromagnetic phase through the radio frequency magnetic field (H) over tilde (rf) in magnetic heterostructures. Time-resolved X-ray magnetic circular dichroism reveals the local phase of the radio frequency magnetic field acting on individual magnetizations (M) over tilde (i) through the susceptibility as (M) over tilde = (chi) over tilde(H) over tilde (rf). An unexpectedly large phase variation, similar to 40 degrees, is detected across spin-valve trilayers driven at 3 GHz. The results have implications for the identification of novel effects in spintronics and suggest general possibilities for electromagnetic-phase profile measurement in heterostructures.

  • 2.
    Berger, Andrew J.
    et al.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Edwards, Eric R. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Nembach, Hans T.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Weiler, Mathias
    Tech Univ Munich, Phys Dept, D-85748 Garching, Germany;Bayerische Akad Wissensch, Walther Meissner Inst, D-85748 Garching, Germany.
    Silva, T. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Determination of the spin Hall effect and the spin diffusion length of Pt from self-consistent fitting of damping enhancement and inverse spin-orbit torque measurements2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 2, article id 024402Article in journal (Refereed)
    Abstract [en]

    Understanding the evolution of spin-orbit torque (SOT) with increasing heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical for the development of magnetic memory based on SOT. However, several experiments have revealed an apparent discrepancy between damping enhancement and dampinglike SOT regarding their dependence on NM thickness. Here, using linewidth and phase-resolved amplitude analysis of vector network analyzer ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract damping enhancement and both fieldlike and dampinglike inverse SOT in Ni80Fe20/Pt bilayers as a function of Pt thickness. By enforcing an interpretation of the data which satisfies Onsager reciprocity, we find that both the damping enhancement and dampinglike inverse SOT can be described by a single spin diffusion length (approximate to 4nm), and that we can separate the spin pumping and spin-memory loss contributions to the total damping. This analysis indicates that less than 40% of the angular momentum pumped by FMR through the Ni80Fe20/Pt interface is transported as spin current into the Pt. On account of the spin-memory loss and corresponding reduction in total spin current available for spin-charge transduction in the Pt, we determine the Pt spin Hall conductivity [sigma(SH) = (2.36 +/- 0.04) x 10(6) omega(-1) m(-1)] and bulk spin Hall angle (theta(SH) = 0.387 +/- 0.008) to be larger than commonly cited values. These results suggest that Pt can be an extremely useful source of SOT if the FM/NM interface can be engineered to minimize spin loss. Lastly, we find that self-consistent fitting of the damping and SOT data is best achieved by a model with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such that both the spin diffusion length and spin Hall conductivity are proportional to the Pt charge conductivity.

  • 3. Choudhury, D.
    et al.
    Mandal, P.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Hazarika, A.
    Rajan, S.
    Sundaresan, A.
    Waghmare, U. V.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Near-Room-Temperature Colossal Magnetodielectricity and Multiglass Properties in Partially Disordered La2NiMnO62012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 12, p. 127201-Article in journal (Refereed)
    Abstract [en]

    We report magnetic, dielectric, and magnetodielectric responses of the pure monoclinic bulk phase of partially disordered La2NiMnO6, exhibiting a spectrum of unusual properties and establish that this compound is an intrinsically multiglass system with a large magnetodielectric coupling (8%-20%) over a wide range of temperatures (150-300 K). Specifically, our results establish a unique way to obtain colossal magnetodielectricity, independent of any striction effects, by engineering the asymmetric hopping contribution to the dielectric constant via the tuning of the relative-spin orientations between neighboring magnetic ions in a transition-metal oxide system. We discuss the role of antisite (Ni-Mn) disorder in emergence of these unusual properties.

  • 4.
    Choudhury, Debraj
    et al.
    Solid State and Structural Chemistry Unit, and Department of Physics, at Indian Institute of Science, Bangalore, Indien.
    Mukherjee, S
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, Indien.
    Mandal, P
    Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Indien.
    Sundaresan, A
    Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Indien.
    Waghamare, U V
    Theoretical Science Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Indien.
    Bhattacharjee, Satadeep
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lazor, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sharma, Ajay
    Department of Physics, Indian Institute of Science, Bangalore, Indien.
    Bhat, S V
    Department of Physics, Indian Institute of Science, Bangalore, Indien.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Tuning of dielectric properties and magnetism of SrTiO3 by site-specific doping of Mn2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 12, p. 125124-Article in journal (Refereed)
    Abstract [en]

    Combining experiments with first-principles calculations, we show that site-specific doping of Mn into SrTiO(3) has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d(0) state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multiglass state in such systems.

  • 5. Coleman, V. A.
    et al.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Grennberg, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Jansson, U.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Quinlan, R.
    Holloway, B. C.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Defect Formation In Graphene Nanosheets By Acid Treatment: An X-Ray Absorption Spectroscopy And Density Functional Theory Study2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 6, p. 062001-4Article in journal (Refereed)
    Abstract [en]

    In-plane defects have been introduced into graphene nanosheets by treatment with hydrochloric acid. Acid treatment induces bond cleavage in the C–C network via electrophilic attack. These resultant vacancy sites will then undergo further reactions with the surrounding ambient to produce C–O and C–H bonds. A σ* resonance at 287 eV in the carbon K-edge x-ray absorption spectra is observed with acid treatment and is assigned to C–O states. Theoretical modelling of a di-vacancy in a graphene bilayer reproduces all essential features of this resonance and in addition predicts a metallic conductivity of states around this vacancy. The possibility of engineering the properties of graphene via the routes explored here is an important step towards establishing strategies for building devices based on this material.

  • 6. Dunn, Jonathan H.
    et al.
    Karis, Olof
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Andersson, Cecilia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Arvanitis, Dimitri
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Carr, R.
    Abrikosov, Igor A.
    Sanyal, Biplab
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Bergqvist, Lars
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Vanishing Magnetic Interactions in Ferromagnetic Thin Films2005In: PHYSICAL REVIEW LETTERS, ISSN 0031-9007, Vol. 94, no 21, p. 217202-Article in journal (Refereed)
    Abstract [en]

    We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.

  • 7.
    Eriksson, O
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV. Physics V. TEORETISK MAGNETISM.
    Andersson, G
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV. Physics V. Fysik III.
    Karis, O
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III. Physics IV. Physics V. Fysik V.
    Svedlindh, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Department of Physics and Materials Science, Physics III. Physics IV. Physics V.
    Lågdimensionell magnetism; en samlingsplats för experiment, teori och industri2001In: Kosmos 2001, 2001, p. 77-Chapter in book (Other (popular scientific, debate etc.))
  • 8. Eyrich, C.
    et al.
    Huttema, W.
    Arora, M.
    Montoya, E.
    Rashidi, F.
    Burrowes, C.
    Kardasz, B.
    Girt, E.
    Heinrich, B.
    Mryasov, O. N.
    From, M.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Exchange stiffness in thin film Co alloys2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 7, p. 07C919-Article in journal (Refereed)
    Abstract [en]

    The exchange stiffness (A(ex)) is one of the key parameters controlling magnetization reversal in magnetic materials. We used a method based on the spin spiral formation in two ferromagnetic films antiferromagnetically coupled across a non-magnetic spacer layer and Brillouin scattering to measure A(ex) for a series of Co1-delta X delta (X=Cr, Ni, Ru, Pd, Pt) thin film alloys. The results show that A(ex) of Co alloys does not necessarily scale with M-s; A(ex) approximately decreases at the rate of 1.1%, 1.5%, 2.1%, 3.5%, and 5.6%, while M-s decreases at the rate of 1.1%, 0.5%, 1.1%, 3.7%, and 2.5% per addition of 1 at% of Pt, Ni, Pd, Cr, and Ru, respectively.

  • 9. Eyrich, C.
    et al.
    Zamani, Atieh
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Huttema, W.
    Arora, M.
    Harrison, D.
    Rashidi, F.
    Broun, D.
    Heinrich, B.
    Mryasov, O.
    Ahlberg, Martina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Jönsson, Petra E.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    From, M.
    Zhu, X.
    Girt, E.
    Effects of substitution on the exchange stiffness and magnetization of Co films2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 23, p. 235408-Article in journal (Refereed)
    Abstract [en]

    An antiferromagnetically coupled FM/NM/FM (FM = ferromagnet, NM = normal metal) trilayer structure responds to an external magnetic field by the formation of a magnetic-moment spring within the FM layers. We show that the exchange stiffness (A ex) of an FM layer can be determined by fitting the field-dependent magnetization, M(H), of the FM/NM/FM trilayer to a micromagnetic model. Using this method, we have measured the exchange stiffness of thin-film Co alloyed with Cr, Fe, Ni, Pd, Pt, and Ru. The results show that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. The observed trends have been understood by material-specific modeling based on density functional theory within the local density approximation. The stiffness measurements are in agreement with Brillouin light scattering carried out on thicker Co films.

  • 10. Girt, Erol
    et al.
    Huttema, W.
    Mryasov, O. N.
    Montoya, E.
    Kardasz, B.
    Eyrich, C.
    Heinrich, B.
    Dobin, A. Yu.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    A method for measuring exchange stiffness in ferromagnetic films2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 7, p. 07B765-Article in journal (Refereed)
    Abstract [en]

    An exchange stiffness, A(ex), in ferromagnetic films is obtained by fitting the M(H) dependence of two ferromagnetic layers antiferromagnetically coupled across a nonmagnetic spacer layer with a simple micromagnetic model. In epitaxial and textured structures this method allows measuring A(ex) between the crystallographic planes perpendicular to the growth direction of ferromagnetic films. Our results show that A(ex) between [0001] planes in textured Co grains is 1.54 +/- 0.12 x 10(-11) J/m.

  • 11.
    Granroth, Sari
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Marcellini, Moreno
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Svensson, Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Gorgoi, Mihaela
    Schäfers, Franz
    Braun, Walter
    Eberhardt, Wolfgang
    Olovsson, Weine
    Holmström, Erik
    Mårtensson, Nils
    Investigation of interface properties of Ni/Cu multilayers by high kinetic energy photoelectron spectroscopy2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 9, article id 094104Article in journal (Refereed)
    Abstract [en]

    High kinetic-energy photoelectron spectroscopy (HIKE) or hard x-ray   photoelectron spectroscopy has been used to investigate the alloying of   Ni/Cu (100) multilayers. Relative intensities of the corelevels and   their chemical shifts derived from binding energy changes are shown to   give precise information on physicochemical properties and quality of   the buried layers. Interface roughening, including kinetic properties   such as the rate of alloying, and temperature effects on the processes   can be analyzed quantitatively. Using HIKE, we have been able to   precisely follow the deterioration of the multilayer structure at the   atomic scale and observe the diffusion of the capping layer into the   multilayer structure which in turn is found to lead to a segregation in   the ternary system. This is of great importance for future research on   multilayered systems of this kind. Our experimental data are   supplemented by first-principles theoretical calculations of the   core-level shifts for a ternary alloy to allow for modeling of the   influence of capping materials on the chemical shifts.

  • 12.
    Granroth, Sari
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Olovsson, Weine
    Holmström, Erik
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Gorgoi, Mihaela
    Svensson, Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Understanding interface properties from high kinetic energy photoelectron spectroscopy and first principles theory2011In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 183, no 1-3, p. 80-93Article, review/survey (Refereed)
    Abstract [en]

    Advances in instrumentation regarding 3rd generation synchrotron light sources and electron spectrometers has enabled the field of high kinetic energy photoelectron spectroscopy (HIKE) (also often denoted hard X-ray photoelectron spectroscopy (HX-PES or HAXPES)). Over the last years, the amount of investigations that relies on the HIKE method has increased dramatically and can arguably be said to have given a rebirth of the interest in photoelectron spectroscopy in many areas. It is in particular the much increased mean free path at higher kinetic energies in combination with the elemental selectivity of the core level spectroscopies in general that has lead to this fact, as it makes it possible to investigate the electronic structure of materials with a substantially reduced surface sensitivity. In this review we demonstrate how HIKE can be used to investigate the interface properties in multilayer systems. Relative intensities of the core level photoelectron peaks and their chemical shifts derived from binding energy changes are found to give precise information on physico-chemical properties and quality of the buried layers. Interface roughening, including kinetic properties such as the rate of alloying, and temperature effects on the processes can be analyzed quantitatively. We will also provide an outline of the theoretical framework that is used to support the interpretation of data. We provide examples from our own investigations of multilayer systems which comprises both systems of more model character and a multilayer system very close to real applications in devices that are considered to be viable alternative to the present read head technology. The experimental data presented in this review is exclusively recorded at the BESSY-II synchrotron at the Helmholtz-Zentrum Berlin fur-Materialien und Energie. This HIKE facility is placed at the bending magnet beamline KMC-1, which makes it different from several other facilities which relies on undulators as the source. We will therefore also briefly describe some of the salient design features of this facility.

  • 13.
    Hahlin, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Andersson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Hunter Dunn, Jonathan
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Arvanitis, Dimitri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Structure and magnetism on in-situ ultrathin epitaxial films: XMCD and EXAFS on Fe/Ag(100)2003In: Proceedings of the 7th International Conference on Nanometer-Scale Science and Technology and the 21st European Conference on Surface Science, 2003, Vol. 532-535, p. 76-81Conference paper (Refereed)
    Abstract [en]

    We have made in situ investigations of epitaxial ultrathin Fe films on Ag(1 0 0). This system is known to exhibit a reorientation of the magnetization, dependent of Fe thickness and temperature. Our aim here is to correlate the local structure with the magnetic properties of this system. The X-ray absorption fine structure has been recorded in situ both in the near edge as well as in the extended X-ray absorption fine structure (EXAFS) range. Using X-ray magnetic circular dichroism we find that, below 300 K, films between 2 and 6 monolayers show an out-of-plane remanent magnetization whereas for thicker films the magnetization lies in-plane. By making use of the Fe L-edge EXAFS we obtain information on the local structure around the Fe atoms, such as the interatomic distances, the coordination number, and the mean square relative displacement of the first neighbor shells.

  • 14.
    Hahlin, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Andersson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Hunter Dunn, Jonathan
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Arvanitis, Dimitri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Structure and magnetism for ultra-thin epitaxial Fe on Ag(100)2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 13, p. 134423-Article in journal (Refereed)
    Abstract [en]

    We have made in-situ investigations of ultrathin films of Fe grown on a Ag(100) single crystal. This system is known to exhibit a reorientation of the magnetization, dependent on both Fe thickness and temperature. X-ray absorption fine structure has been recorded for samples prepared in-situ, both in the near edge and in the extended x-ray absorption fine structure (EXAFS) region. Using x-ray magnetic circular dichroism we found that Fe films between 2–5 monolayers show an out-of-plane remanent magnetization. For thicker films the magnetization lies in-plane. By applying the magneto-optical sum rules we found an enhancement of the orbital moment (ml) for the out-of-plane phase, whereas the spin moment (ms) is unchanged. From the Fe L-edge EXAFS, we obtain information on the local crystallographic structure. A strong correlation between the local crystallographic structure and the magnetic properties is found for the Fe∕Ag(100) system. Variations in the nearest neighbor distance of ∼0.15 Å are observed when comparing 3 ML and 25 ML films. By comparison to simulations performed with the FEFF 8.10 code, we can identify a bcc structure for 6–25 ML Fe on Ag(100). For the 3 ML Fe film our simulations indicate strong deviations from any structure derived along the Bain path. We conclude that intermixing and distortion are important to describe the structure in this thickness range.

  • 15. Hallin, A.
    et al.
    Andersson, C.
    Dunn, J. H.
    Sanyal, Biplab
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics V.
    Karis, Olof
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics V.
    Arvanitis, Dimitri
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics V.
    Structure and magnetism of ultrathin epitaxial Fe on Ag(100)2006In: Phys. Rev., B, Condens, Matter Mater. Phys. (USA), Vol. 73(13), no 134423Article in journal (Refereed)
  • 16. Holmström, E.
    et al.
    Olovsson, W.
    Abrikosov, I. A.
    Niklasson, A. M. N.
    Johansson, B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Gorgoi, M.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Svensson, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Schäfers, F.
    Braun, W.
    Öhrwall, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Marcellini, Moreno
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eberhardt, W.
    Sample preserving deep interface characterization technique2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 26, article id 266106Article in journal (Refereed)
    Abstract [en]

    We propose a nondestructive technique based on atomic core-level shifts to characterize the interface quality of thin film nanomaterials. Our method uses the inherent sensitivity of the atomic core-level binding energies to their local surroundings in order to probe the layer-resolved binary alloy composition profiles at deeply embedded interfaces. From an analysis based upon high energy x-ray photoemission spectroscopy and density functional theory of a Ni/Cu fcc (100) model system, we demonstrate that this technique is a sensitive tool to characterize the sharpness of a buried interface. We performed controlled interface tuning by gradually approaching the diffusion temperature of the multilayer, which lead to intermixing. We show that core-level spectroscopy directly reflects the changes in the electronic structure of the buried interfaces, which ultimately determines the functionality of the nanosized material.

  • 17. Hunter Dunn, J.
    et al.
    Hahlin, Anders
    Karis, Olof
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics V.
    Arvanitis, Dimitri
    Department of Physics and Materials Science, Physics V.
    Le Blanc, G.
    Andersson, Å.
    Lindgren, L. -J
    Elliptically polarised soft X-rays produced using a local bump in MAX II characterisation of the degree of polarisation,2004In: AIP Conference Proceedings, Vol. 65-8, p. 708-Article in journal (Refereed)
  • 18.
    Iusan, Diana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Coleman, Victoria A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Westin, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Wikberg, J. Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electronic structure and chemical and magnetic interactions in ZnO doped with Co and Al: Experiments and ab initio density-functional calculations2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 8, p. 085319-Article in journal (Refereed)
    Abstract [en]

    We present results of electronic structure and magnetization measurements of Co:ZnO and Co:ZnO codoped with Al thin-film samples fabricated by solution-based methods together with ab initio electronic structure calculations. Electronic structure measurements indicate that the Co states lie close to the valence-band edge with pinning of the Fermi level primarily due to native defects yielding a heavily n-doped material. The findings in the electronic structure measurements are corroborated by results from theoretical calculations. We find that it is necessary to go beyond the local-density approximation to achieve agreement with experiments. Moreover, the theoretical calculations indicate a tendency for the formation of Co clusters, giving rise to an antiferromagnetic exchange interaction between the Co atoms. The magnetization measurements are well in line with the theoretical predictions, showing a dominating superparamagnetic behavior arising from small antiferromagnetic clusters containing uncompensated spins.

  • 19.
    Iusan, Diana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Coleman, Victoria A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Westin, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Wikberg, J. Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electronic structure and chemical and magnetic interactions in ZnO doped with Co and Al: Experiments and ab initio density-functional calculations2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 8, p. 085319-Article in journal (Refereed)
    Abstract [en]

    We present results of electronic structure and magnetization measurements of Co:ZnO and Co:ZnO codoped with Al thin-film samples fabricated by solution-based methods together with ab initio electronic structure calculations. Electronic structure measurements indicate that the Co states lie close to the valence-band edge with pinning of the Fermi level primarily due to native defects yielding a heavily n-doped material. The findings in the electronic structure measurements are corroborated by results from theoretical calculations. We find that it is necessary to go beyond the local-density approximation to achieve agreement with experiments. Moreover, the theoretical calculations indicate a tendency for the formation of Co clusters, giving rise to an antiferromagnetic exchange interaction between the Co atoms. The magnetization measurements are well in line with the theoretical predictions, showing a dominating superparamagnetic behavior arising from small antiferromagnetic clusters containing uncompensated spins.

  • 20.
    Jain, Sagar M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Davies, Matthew L.
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Li, Meng
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales;Soochow Univ, Inst Funct Nano & Soft Mat, Suzhou 215000, Peoples R China.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    De Castro, Catherine
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Qiu, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kim, Jinhyun
    Imperial Coll London, Dept Chem, Exhibit Rd, London SW7 2AZ, England;Imperial Coll London, Ctr Plast Elect, Exhibit Rd, London SW7 2AZ, England.
    Watson, Trystan
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Tsoi, Wing Chung
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Durrant, James R.
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales;Imperial Coll London, Dept Chem, Exhibit Rd, London SW7 2AZ, England;Imperial Coll London, Ctr Plast Elect, Exhibit Rd, London SW7 2AZ, England.
    An effective approach of vapour assisted morphological tailoring for reducing metal defect sites in lead-free, (CH3NH3)(3)Bi2I9 bismuth-based perovskite solar cells for improved performance and long-term stability2018In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 49, p. 614-624Article in journal (Refereed)
    Abstract [en]

    We present a controlled, stepwise formation of methylammonium bismuth iodide (CH3NH3)(3)Bi2I9 perovskite films prepared via the vapour assisted solution process (VASP) by exposing BiI3 films to CH3NH3I (MAI) vapours for different reaction times, (CH3NH3)(3)Bi2I9 semiconductor films with tunable optoelectronic properties are obtained. Solar cells prepared on mesoporous TiO2 substrates yielded hysteresis-free efficiencies upto 3.17% with good reproducibility. The good performance is attributed mainly to the homogeneous surface coverage, improved stoichiometry, reduced metallic content in the bulk, and desired optoelectronic properties of the absorbing material. In addition, solar cells prepared using pure BiI3 films without MAI exposure achieved a power conversion efficiency of 0.34%. The non-encapsulated (CH3NH3)(3)Bi2I9 devices were found to be stable for as long as 60 days with only 0.1% drop in efficiency. This controlled formation of (CH3NH3)(3)Bi2I9 perovskite films highlights the benefit of the VASP technique to optimize material stoichiometry, morphology, solar cell performance, and long-term durability.

  • 21.
    Jana, Somnath
    et al.
    Centre for Advanced Materials, Indian Association for the Cultivation of Science, Jadavpur, India.
    Meneghini, Carlo
    Sanyal, Prabuddha
    Sarkar, Soumyajit
    Saha-Dasgupta, Tanusri
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Ray, Sugata
    Signature of an antiferromagnetic metallic ground state in heavily electron-doped Sr2FeMoO62012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 5, p. 054433-Article in journal (Refereed)
    Abstract [en]

    Sr2FeMoO6 is a well-known double perovskite with exciting high-temperature magnetic properties. Through various magnetic and spectroscopic measurements, we collect compelling evidence here that this compound can be driven into a rare three-dimensional antiferromagnetic metallic state by heavy electron doping (70% Sr2+ substitution by La3+). Moreover, local structural study of these Sr2-xLaxFeMoO6 (1.0 <= x <= 1.5) compounds reveals unusual atomic scale phase distribution in terms of La,Fe- and Sr,Mo-rich regions driven by strong La-O covalency, a phenomenon hitherto undisclosed in double perovskites. The general trend of our findings is in agreement with theoretical calculations carried out on realistic structures having local chemical fluctuations, which reconfirms the relevance of the kinetic-energy-driven magnetic model.

  • 22.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India;Helmholtz Zentrum Berlin FG ISRR, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Panda, S. K.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Bennett Univ, Dept Phys, Greater Noida 201310, Uttar Pradesh, India.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Pal, B.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Dutta, A.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Anil Kumar, Puri
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Segre, Carlo U.
    IIT, CSRRI, Chicago, IL 60616 USA;IIT, Dept Phys, Chicago, IL 60616 USA.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Biermann, S.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Coll France, 11 Pl Marcelin Berthelot, F-75005 Paris, France.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sarma, D. D.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO32019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed)
    Abstract [en]

    We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.

  • 23.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Panda, Swarup
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Pal, Banabir
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Dutta, Anirban
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Segre, Carlo U.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Biermann, Silke
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Sarma, D.D.
    Doping induced site-selective Mott insulating phase in LaFeO3Manuscript (preprint) (Other academic)
    Abstract [en]

    Tailoring transport properties of strongly correlated electron systems in a controlled fashion counts among the dreams of materials scientists. In copper oxides, vary- ing the carrier concentration is a tool to obtain high- temperature superconducting phases. In manganites, dop- ing results in exotic physics such as insulator-metal tran- sitions (IMT), colossal magnetoresistance (CMR), orbital- or charge-ordered (CO) or charge-disproportionate (CD) states. In most oxides, antiferromagnetic order and CD phase is asssociated with insulating behavior. Here we re- port the realization of a unique physical state that can be induced by Mo doping in LaFeO3: the resulting metallic state is a site-selective Mott insulator where itinerant elec- trons evolving on low-energy Mo states coexist with local- ized carriers on the Fe sites. In addition, a local breathing- type lattice distortion induces charge disproportionation on the latter, without destroying the antiferromagnetic order. A state, combining antiferromangetism, metallic- ity and CD phenomena is rather rare in oxides and have utmost significance for future antiferromagnetic memory devices.

  • 24.
    Jana, Somnath
    et al.
    Centre for Advanced Materials, Indian Association for the Cultivation of Science, Jadavpur, India.
    Singh, Vijay
    Kaushik, S. D.
    Meneghini, Carlo
    Pal, Prabir
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Dasgupta, Indra
    Siruguri, Vasudeva
    Ray, Sugata
    Atomic-scale chemical fluctuation in LaSrVMoO6, a proposed half-metallic antiferromagnet2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 18, article id 180407Article in journal (Refereed)
    Abstract [en]

    Half-metallic antiferromagnets (HMAFMs) have been proposed theoretically long ago but have not been realized experimentally yet. Recently, a double perovskite compound, LaSrVMoO6, has been claimed to be an almost real HMAFM system. Here, we report detailed experimental and theoretical studies on this compound. Our results reveal that the compound is neither a half-metal nor an ordered antiferromagnet. Most importantly, an unusual chemical fluctuation is observed locally, which finally accounts for all the electronic and magnetic properties of this compound.

  • 25.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Terschlüsen, Joachim A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Stefanuik, Robert
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Plogmaker, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. MAX VI Lab, Lund, Sweden..
    Troisi, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Malik, Rameez S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Svanqvist, Mathias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Swedish Def Res Agcy, FOI, SE-14725 Tumba, Sweden..
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    A setup for element specific magnetization dynamics using the transverse magneto-optic Kerr effect in the energy range of 30-72 eV2017In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 88, no 3, article id 033113Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a spectrometer that is designed for element-specific and time-resolved transverse magneto-optic Kerr effect experiments at the high-harmonic generation pump-probe facility High Energy Laser Induced Overtone Source (HELIOS) laboratory. HELIOS delivers photons with energies between 30 eV and 72 eV with an overall time resolution of less than 40 fs. The spectrometer is based on a Rowland-circle geometry and allows for simultaneous measurements of all magnetic transition-metal elements. The setup also features easy sample transfer and alignment, and it combines high photon throughput, optimized data acquisition, and a fast switching of the magnetic field at the sample. The spectrometer performance is demonstrated by measuring the ultrafast demagnetization of permalloy. Our data are, for all practical purposes, identical to what have been reported in the earlier high-order harmonic generation work of a similar sample by Mathias et al. [Proc. Natl. Acad. Sci. U.S.A. 109, 4792-4797 (2012)], however, obtained within 15% of the acquisition time compared to their study. Furthermore, our data show a shift of the demagnetization curve of Ni relative to Fe, which has previously been interpreted as a delay of the Ni demagnetization to that of Fe [S. Mathias et al., Proc. Natl. Acad. Sci. U. S. A. 109, 4792-4797 (2012)].

  • 26.
    Kadas, Krisztina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Andersson, Matilda
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Holmström, Erik
    Wende, Heiko
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Urbonaite, Sigita
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Nikitenko, Sergey
    Kvashnina, Kristina O.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Structural properties of amorphous metal carbides: Theory and experiment2012In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 12, p. 4720-4728Article in journal (Refereed)
    Abstract [en]

    By means of theoretical modeling and experimental synthesis and characterization, we investigate the structural properties of amorphous Zr-Si-C. Two chemical compositions are selected: Zr0.31Si0.29C0.40 and Zr0.60Si0.33C0.07. Amorphous structures are generated in the theoretical part of our work by the stochastic quenching (SQ) method, and detailed comparison is made regarding the structure and density of the experimentally synthesized films. These films are analyzed experimentally using X-ray absorption spectroscopy, transmission electron microscopy and X-ray diffraction. Our results demonstrate a remarkable agreement between theory and experiment concerning bond distances and atomic coordination of this complex amorphous metal carbide. The demonstrated power of the SQ method opens up avenues for theoretical predictions of amorphous materials in general.

  • 27.
    Karis, O
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Magnuson, Martin
    Wiell, T
    Weinelt, M
    Wassdahl, N
    Nilsson, A
    Martensson, N
    Holmstrom, E
    Niklasson, AMN
    Eriksson, O
    Observation of short- and long-range hybridization of a buried Cu monolayer in Ni2000In: PHYSICAL REVIEW B, ISSN 0163-1829, Vol. 62, no 24, p. R16239-R16242Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a Cu monolayer buried in Ni fcc(100) is studied by means of x-ray emission and absorption spectroscopies in combination with first principles calculations. The local character of the x-ray probes allows us to investigate change

  • 28.
    Karis, O
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Magnuson, Martin
    Wiell, T
    Weinelt, M
    Wassdahl, N
    Nilsson, A
    Martensson, N
    Holmstrom, E
    Niklasson, AMN
    Eriksson, O
    Johansson, B
    Probing surface states of Cu/Ni thin films using x-ray absorption spectroscopy - art. no. 1134012001In: PHYSICAL REVIEW B, ISSN 0163-1829, Vol. 6311, no 11, p. 3401-+Article in journal (Refereed)
    Abstract [en]

    Surface and interface properties of Cu thin films (1-4 monolayers) deposited on Ni(100) have been extracted by means of x-ray absorption spectroscopy and analyzed in combination with ab initio density-functional calculations. An unoccupied Cu surface stat

  • 29.
    Karis, Olof
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry.
    Valizadeh, Sima
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry. Elektronmikroskopi.
    Surpi, Alessandro
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry. Istituto di Fotonica e Nanotecnologie (C.N.R.).
    HUNTER DUNN, J
    MAX-lab, Lund, Sweden..
    SVEDLINDH, PETER
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry.
    Stanciu, V
    Warnicke, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry.
    Sandell, Anders
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry.
    Nyholm, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry. oorganisk kemi.
    Sanyal, Biplab
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Materials Science, Experimental Physics. Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry. Technology, Department of Engineering Sciences, Solid State Physics. Department of Materials Chemistry, Inorganic Chemistry.
    Electronic and geometric structure of (Zn,Co)O room temperature Ferromagnets2005In: 50th MMM Meeting Program, 2005Conference paper (Refereed)
  • 30.
    Knut, Ronny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Spectroscopic investigations of electronic structure2012In: Advanced Functional Materials: A Perspective from Theory and Experiment / [ed] Tara Prasad Das, Biplab Sanyal and Olle Eriksson, Elsevier, 2012, no 1, p. 45-70Chapter in book (Refereed)
  • 31.
    Knut, Ronny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lagerqvist, Ulrika
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Palmgren, Pål
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Pal, P.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pohl, Annika
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Photoinduced reduction of surface states in Fe:ZnO2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 20, article id 204703Article in journal (Refereed)
    Abstract [en]

    We report on the electronic structure of nano-crystalline Fe:ZnO, which has recently been found to be an efficient photocatalyst. Using resonant photoemission spectroscopy, we determine the binding energy of Fe 3d states corresponding to different valencies and coordination of the Fe atoms. The photo-activity of ZnO reduces Fe from 3+ to 2+ in the surface region of the nano-crystalline material due to the formation of oxygen vacancies. Electronic states corresponding to low-spin Fe2+ are observed and attributed to crystal field modification at the surface. These states are potentially important for the photocatalytic sensitivity to visible light due to their location deep in the ZnO bandgap. X-ray absorption and x-ray photoemission spectroscopy suggest that Fe is only homogeneously distributed for concentrations up to 3%. Increased concentrations does not result in a higher concentration of Fe ions in the surface region. This is limiting the photocatalytic functionality of ZnO, where the most efficient Fe doping concentration has been shown to be 1%-4%.

  • 32.
    Knut, Ronny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lindblad, Rebecka
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Gorgoi, Mihaela
    Rensmo, Hakan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    High energy photoelectron spectroscopy in basic and applied science: Bulk and interface electronic structure2013In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 190, p. 278-288Article in journal (Refereed)
    Abstract [en]

    With the access of new high-performance electron spectrometers capable of analyzing electron energies up to the order of 10 keV, the interest for photoelectron spectroscopy has grown and many new applications of the technique in areas where electron spectroscopies were considered to have limited use have been demonstrated over the last few decades. The technique, often denoted hard X-ray photoelectron spectroscopy (HX-PES or HAXPES), to distinguish the experiment from X-ray photoelectron spectroscopy performed at lower energies, has resulted in an increasing interest in photoelectron spectroscopy in many areas. The much increased mean free path at higher kinetic energies, in combination with the elemental selectivity of the core level spectroscopies in general has led to this fact. It is thus now possible to investigate the electronic structure of materials with a substantially enhanced bulk sensitivity. In this review we provide examples from our own research using HAXPES which to date has been performed mainly at the HIKE facility at the KMC-1 beamline at HZB, Berlin. The review exemplifies the new opportunities using HAXPES to address both bulk and interface electronic properties in systems relevant for applications in magnetic storage, energy related research, but also in purely curiosity driven problems.

  • 33.
    Knut, Ronny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lindblad, Rebecka
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Gorgoi, Mihaela
    Rensmo, Hakan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    High energy photoelectron spectroscopy in basic and applied science: Bulk and interface electronic structure2013In: Journal of Electron Spectroscopy and Related Phenomena, Vol. 190, p. 278-288Article in journal (Refereed)
  • 34.
    Knut, Ronny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lindblad, Rebecka
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Grachev, Sergey
    Faou, Jean-Yvon
    Gorgoi, Mihaela
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Søndergård, Elin
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Reactive ZnO/Ti/ZnO interfaces studied by hard x-ray photoelectron spectroscopy2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 4, p. 043714-043714-7Article in journal (Refereed)
    Abstract [en]

    The chemistry and intermixing at buried interfaces in sputter deposited ZnO/Ti/ZnO thin layers were studied by hard x-ray photoelectron spectroscopy. The long mean free path of the photoelectrons allowed for detailed studies of the oxidation state, band bending effects, and intrinsic doping of the buried interfaces. Oxidation of the Ti layer was observed when ZnO was deposited on top. When Ti is deposited onto ZnO, Zn Auger peaks acquire a metallic character indicating a strong reduction of ZnO at the interface. Annealing of the stack at 200 °C results in further reduction of ZnO and oxidation of Ti. Above 300 °C, oxygen transport from the bulk of the ZnO layer takes place, leading to re-oxidation of ZnO at the interface and further oxidation of Ti layer. Heating above 500 °C leads to an intermixing of the layers and the formation of a ZnxTiOy compound.

  • 35.
    Knut, Ronny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mryasov, Oleg
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Warnicke, Peter
    Arena, D. A.
    Björck, Matts
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Dennison, Andrew J. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Sahoo, Anindita
    Mukherjee, Sumanta
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Granroth, Sari
    Gorgoi, Mihaela
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 13, p. 134407-Article in journal (Refereed)
    Abstract [en]

    To address the amount of disorder and interface diffusion induced by annealing, all-Heusler multilayer structures, consisting of ferromagnetic Co2MnGe and nonmagnetic Rh2CuSn layers of varying thicknesses, have been investigated by means of hard x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism. We find evidence for a 4 angstrom thick magnetically dead layer that, together with the identified interlayer diffusion, are likely reasons for the unexpectedly small magnetoresistance found for current-perpendicular-to-plane giant magnetoresistance devices based on this all-Heusler system. We find that diffusion begins already at comparably low temperatures between 200 and 250 degrees C, where Mn appears to be most prone to diffusion.

  • 36.
    Knut, Ronny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Wikberg, J. Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lashgari, Koroush
    Coleman, Victoria A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Westin, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Magnetic and electronic characterization of highly Co-doped ZnO: An annealing study at the solubility limit2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 9, p. 094438-Article in journal (Refereed)
    Abstract [en]

    We report on investigations of the electronic structure and magnetic properties of ZnO doped with 15 at. % Co and postgrowth annealed at temperatures ranging between 250 and 800°C. In particular, we demonstrate how the presence of Co3+, indicative of secondary phases, is manifested in spectroscopy. Through resonant photoemmision spectroscopy we have found that x-ray diffraction in some cases underestimates or does not reveal the presence of secondary phases, possibly due to unrelaxed structures or structural arrangements with sizes below the detection limit. The magnetic properties are in most cases understood by assuming small antiferromagnetic clusters but can also show a behavior indicative of ferromagnetic interactions.

  • 37.
    Kumar, P. Anil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Vijayaraghavan, R.
    Majumdar, Subham
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ferrimagnetism, antiferromagnetism, and magnetic frustration in La2-xSrxCuRuO6 (0 <= x <= 1)2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 9, p. 094421-Article in journal (Refereed)
    Abstract [en]

    We studied structural and magnetic properties of a series of insulating double perovskite compounds, La2-xSrxCuRuO6 (0 <= x <= 1), representing doping via A-site substitution. The end members La2CuRuO6 and LaSrCuRuO6 form in monoclinic structure while the intermediate Sr doped compounds stabilize in triclinic structure. The Cu and Ru ions sit on alternate B sites of the perovskite lattice with similar to 15% antisite defects in the undoped sample while the Sr-doped samples show a tendency to higher ordering at B sites. The undoped (x = 0) compound shows a ferrimagnetic-like behavior at low temperatures. In surprising contrast to the usual expectation of an enhancement of ferromagnetic interaction on doping, an antiferromagnetic-like ground state is realized for all doped samples (x > 0). Heat capacity measurements indicate the absence of any long-range magnetic order in any of these compounds. The magnetic relaxation and memory effects observed in all compounds suggest glassy dynamical properties associated with magnetic disorder and frustration. We show that the observed magnetic properties are dominated by the competition between the nearest-neighbor Ru-O-Cu 180 degrees superexchange interaction and the next-nearest-neighbor Ru-O-O-Ru 90 degrees superexchange interaction as well as by the formation of antisite defects with interchanged Cu and Ru positions. Our calculated exchange interaction parameters from first principles calculations for x = 0 and x = 1 support this interpretation.

  • 38.
    Kumar Puri, Anil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ray, Sugata
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Reentrant Superspin Glass Phase in a La0.82Ca0.18MnO3 Ferromagnetic Insulator2014In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 4, no 1, p. 011037-Article in journal (Refereed)
    Abstract [en]

    We report results of the magnetization and ac susceptibility measurements down to very low fields on a single crystal of the perovskite manganite, La-0.82 Ca-0.18 MnO3. This composition falls in the intriguing ferromagnetic insulator region of the manganite phase diagram. In contrast to earlier beliefs, our investigations reveal that magnetically (and in every other sense), this is a single- phase system with a ferromagnetic ordering temperature of around 170 K. However, this ferromagnetic state is magnetically frustrated, and the system exhibits pronounced glassy dynamics below 90 K. Based on measured dynamical properties, we propose that this quasi-long-ranged ferromagnetic phase, and the associated superspin glass behavior, is the true magnetic state of the system, rather than being a macroscopic mixture of ferromagnetic and antiferromagnetic phases, as often suggested. Our results provide an understanding of the quantum phase transition from an antiferromagnetic insulator to a ferromagnetic metal via this ferromagnetic state as a function of x in La1-xCaxMnO3, in terms of the possible formation of magnetic polarons.

  • 39.
    Lindblad, Rebecka
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Jena, Naresh K
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Oscarsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Bi, Dongqin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Mandal, Suman
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.
    Pal, Banabir
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.
    Sarma, Dipankar Das
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Siegbahn, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Johansson, Erik M.J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Odelius, Michael
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Electronic Structure of CH3NH3PbX3 Perovskites: Dependence on the Halide Moiety2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 4, p. 1818-1825Article in journal (Refereed)
    Abstract [en]

    A combination of measurements using photoelectron spectroscopy and calculations using density functional theory (DFT) was applied to compare the detailed electronic structure of the organolead halide perovskites CH3NH3PbI3 and CH3NH3PbBr3. These perovskite materials are used to absorb light in mesoscopic and planar heterojunction solar cells. The Pb 4f core level is investigated to get insight into the chemistry of the two materials. Valence level measurments are also included showing a shift of the valence band edges where there is a higher binding energy of the edge for the CH3NH3PbBr3 perovskite. These changes are supported by the theoretical calculations which indicate that the differences in electronic structure are mainly caused by the nature of the halide ion rather than structural differences. The combination of photoelectron spectroscopy measurements and electronic structure calculations is essential to disentangle how the valence band edge in organolead halide perovskites is governed by the intrinsic difference in energy levels of the halide ions from the influence of chemical bonding.

  • 40.
    Martensson, N
    et al.
    Uppsala University.
    Weinelt, M
    Karis, O
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Wassdahl, N
    Nilsson, A
    Stohr, J
    Samant, M
    Coherent and incoherent processes in resonant photoemission1997In: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, ISSN 0947-8396, Vol. 65, no 2, p. 159-167Article in journal (Other scientific)
    Abstract [en]

    The basis for resonant photoemission is discussed in connection with data for a physisorption system, Ar/Pt(111) and a 3d transition metal, Ni(100). For Ar/Pt(111) the quasi-localized character of the intermediate state leads to two types of features in t

  • 41. Mazumdar, Dipanjan
    et al.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Thöle, F.
    Gorgoi, M.
    Faleev, Sergei
    Mryasov, O. N.
    Shelke, Vilas
    Ederer, C.
    Spaldin, N. A.
    Gupta, A.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    The valence band electronic structure of rhombohedral-like and tetragonal-like BiFeO3 thin films from hard X-ray photoelectron spectroscopy and first-principles theory2016In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 208, p. 63-66Article in journal (Refereed)
    Abstract [en]

    Abstract We investigate the electronic structure of rhombohedral-like (R) and tetragonal-like (T) BiFeO3 thin films using high energy X-ray photoelectron spectroscopy and first-principles electronic structure calculations. By exploiting the relative elemental cross sections to selectively probe the elemental composition of the valence band, we identify a strong Bi 6p contribution at the top of the valence band in both phases, overlapping in energy range with the O 2p states; this assignment is confirmed by our electronic structure calculations. We find that the measured occupied Bi 6p signal lies closer to the top of the valence band in the T phase than in the R phase, which we attribute, using our electronic structure calculations, to lower Bi–O hybridization in the T phase. We note, however, that our calculations of the corresponding densities of states underestimate the difference between the phases, suggesting that matrix element effects resulting from the different effective symmetries also contribute. Our results shed light on the chemical nature of the stereochemically active Bi lone pairs, which are responsible for the large ferroelectric polarization of BiFeO3.

  • 42.
    Mukherjee, S.
    et al.
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Mohseni, S. M.
    Anh Nguyen, T. N.
    Chung, S.
    Tuan Le, Q.
    Åkerman, J.
    Persson, J.
    Sahoo, A.
    Hazarika, A.
    Pal, B.
    Thiess, S.
    Gorgoi, M.
    Anil Kumar, P. S.
    Drube, W.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sarma, D. D.
    Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, ISSN 1098-0121, Vol. 91, no 8, article id 085311Article in journal (Refereed)
    Abstract [en]

    Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.

  • 43. Mukherjee, Sumanta
    et al.
    Hazarika, Abhijit
    Santra, Pralay K.
    Abdelhady, Ahmed L.
    Malik, Mohammad Azad
    Gorgoi, Mihaela
    O'Brien, P.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Determination of Internal Structures of Heterogeneous Nanocrystals Using Variable-Energy Photoemission Spectroscopy2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 28, p. 15534-15540Article in journal (Refereed)
    Abstract [en]

    This article describes the determination of the internal structure of heterogeneous nanoparticle systems including inverted core-shell (CdS core and CdSe shell) and alloyed (CdSeS) quantum dots using depth-resolved, variable-energy X-ray photoelectron spectroscopy (XPS). A unique feature of this work is the combination of photoelectron spectroscopy performed at lower X-ray energies (400-700 eV), to achieve surface sensitivity, with bulk sensitive measurements at high photon energies (>2000 eV), thereby providing detailed information about the whole nanoparticle structure with a great accuracy. The use of high photon energies furthermore allows us to investigate nanoparticles much larger than those studied thus far. This capability is a consequence of the much-increased mean free path of the photoelectron achieved at high excitation energies. Our results show that the actual structures of the synthesized nanoparticles are considerably different from the nominal, targeted structures, which can be post facto rationalized in terms of the reactivity of different constituents.

  • 44.
    Mukherjee, Sumanta
    et al.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, Karnataka, India..
    Pal, Banabir
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, Karnataka, India..
    Choudhury, Debraj
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, Karnataka, India.;Indian Inst Technol, Dept Phys, Kharagpur 721302, W Bengal, India..
    Sarkar, Indranil
    Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany..
    Drube, Wolfgang
    Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany..
    Gorgoi, Mihaela
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Takagi, H.
    Univ Tokyo, Dept Phys, Tokyo 1130033, Japan.;Max Plank Inst Solid State Res, D-70569 Stuttgart, Germany..
    Matsuno, Jobu
    RIKEN, CEMS, 2-1 Hirosawa, Wako, Saitama 3510198, Japan..
    Sarma, D. D.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, Karnataka, India.;Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;CSIR, NISE, New Delhi 110001, India.;Jawaharlal Nehru Ctr Adv Sci Res, Bengaluru 560064, India..
    Origin and distribution of charge carriers in LaAlO3-SrTiO3 oxide heterostructures in the high carrier density limit2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 24, article id 245124Article in journal (Refereed)
    Abstract [en]

    Using hard x-ray photoelectron spectroscopywith variable photon energy (2-8 keV), we address the distribution of charge carriers in the prototypical LaAlO3 (LAO) and SrTiO3 (STO) oxide heterostructures with high carrier densities (10(17) cm(-2)). Our results demonstrate the presence of two distinct charge distributions in this system: one tied to the interface with a similar to 1-nm width and similar to 2-5 x 10(14)-cm(-2) carrier concentration, while the other appears distributed nearly homogeneously through the bulk of STO corresponding to a much larger carrier contribution. Our results also establish bimodal oxygen vacancies, namely on top of LAO and throughout STO, quantitatively establishing these as the origin of the observed bimodal depth distribution of charge carriers in these highly doped sample.

  • 45. Nguyen, T. N. Anh
    et al.
    Knut, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Fallahi, V.
    Chung, S.
    Le, Q. Tuan
    Mohseni, S. M.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Peredkov, S.
    Dumas, R. K.
    Miller, Casey W.
    Akerman, J.
    Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs2014In: Physical Review Applied, ISSN 2331-7019, Vol. 2, no 4, p. 044014-Article in journal (Refereed)
    Abstract [en]

    We report on the magnetization depth profile of a hybrid exchange-spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element-specific x-ray magnetic circular dichroism of the Fe and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.

  • 46. Nguyen, T. N. Anh
    et al.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Fallahi, V.
    Chung, S.
    Le, Q. Tuan
    Mohseni, S.  M.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Peredkov, S.
    Dumas, R.  K.
    Miller, Casey W.
    Åkerman, J.
    Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs2014In: Physical Review Applied, Vol. 2, no 4Article in journal (Refereed)
  • 47.
    Pal, Somnath
    et al.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Govinda, Sharada
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Goyal, Manik
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Mukherjee, Soham
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Pal, Banabir
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Saha, Rana
    Jawaharlal Nehru Ctr Adv Sci Res, Chem & Phys Mat Unit, Bengaluru 560064, India.
    Sundaresan, A.
    Jawaharlal Nehru Ctr Adv Sci Res, Chem & Phys Mat Unit, Bengaluru 560064, India.
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Freeland, John W.
    Argonne Natl Lab, Argonne, IL 60439 USA.
    Sarma, D. D.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India;Jawaharlal Nehru Ctr Adv Sci Res, Bengaluru, India.
    Effect of anti-site disorder on magnetism in La2NiMnO62018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 16, article id 165137Article in journal (Refereed)
    Abstract [en]

    La2NiMnO6 has been reported to exhibit a paramagnetic to ferromagnetic transition with a transition temperature of similar to 260 K. However, most of its magnetic properties, such as the saturation magnetization and even the transition temperature, appear to vary considerably among different reports. This is possibly because the crystallographic structure as well as the extent of the anti-site disorder (ASD) at the Ni/Mn sites are strongly influenced by the choice of synthesis routes. There are diverse reports connecting the extent of ASD to the valencies of Ni and Mn ions, such as Ni2+-Mn4+ and Ni3+-Mn3+, including suggestions of thermally induced valence transitions. Consequently, these reports arrive at very different conclusions on the mechanism behind the magnetic properties of La2NiMnO6. To address the correlation between ASD and valency, we have carried out a comparative study of two monoclinic La2NiMnO6 polycrystals with different degrees of ASD. Using a combination of x-ray absorption spectroscopy, x-raymagnetic circular dichroism, andmagnetometry, we conclude that the valency of the transition metal ions, and the transition temperature, are insensitive to the extent of ASD. However, we find the magnetic moment decreases strongly with an increasing ASD. We attribute this effect to the introduction of antiferromagnetic interactions in the anti-site disordered regions.

  • 48.
    Pal, Somnath
    et al.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Helmholtz Zentrum Berlin Mat & Energie, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Govinda, Sharada
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Pal, Banabir
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Mukherjee, Sumanta
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Keshavarz, Samara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thonig, Danny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Freeland, John W.
    Argonne Natl Lab, Argonne, IL 60439 USA.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Sarma, D. D.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India;Jawaharlal Nehru Ctr Adv Sci Res, Bengaluru, India.
    Peculiar magnetic states in the double perovskite Nd2NiMnO62019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 4, article id 045122Article in journal (Refereed)
    Abstract [en]

    We present magnetic measurements on Nd2NiMnO6 which exhibits a well-known insulating paramagnetic state to an insulating ferromagnetic state transition when cooled below 200 K. Beyond this basic fact, there is a great deal of diversity in the reported magnetic properties and interpretation of specific anomalies observed in the magnetic data of this compound below the Curie temperature. We address specifically two anomalies discussed in the past, namely, a spin-glass like behavior observed in some samples near 100 K and a downturn in the magnetization with a lowering of the temperature below approximately 50 K. We show for the first time that the application of an increasing magnetic field can systematically change the low-temperature behavior to make the down-turn in the magnetization into an upturn. With the help of first principle calculations and extensive simulations along with our experimental observations, we provide a microscopic understanding of all magnetic properties observed in this interesting system to point out that the glassiness around 100 K is absent in well-ordered samples and that the low-temperature magnetic anomaly below 50 K is a consequence of a ferromagnetic coupling of the Nd spin moments with the spin of the Ni-Mn ordered sublattice without giving rise to any ordering of the Nd sublattice that remains paramagnetic, contrary to earlier claims. We explain this counter-intuitive interpretation of a ferromagnetic coupling of Nd spins with Ni-Mn spin giving rise to a decrease in the total magnetic moment by noting the less than half-filled 4f occupation of Nd that ensures orbital and spin moments of Nd to be opposite to each other due to the spin-orbit coupling. Since the ground state total magnetic moment of Nd has a contribution from the orbital moment, that is larger than the spin moment, the total moment of Nd is indeed pointing in a direction opposite to the direction of spin moments of the Ni-Mn sublattice as a consequence of the ferromagnetic exchange coupling between Nd and Ni-Mn spins.

  • 49.
    Panda, Swarup K.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pal, Banabir
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India..
    Mandal, Suman
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India..
    Gorgoi, Mihaela
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Das, Shyamashis
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India..
    Sarkar, Indranil
    Deutsches Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany..
    Drube, Wolfgang
    Deutsches Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany..
    Sun, Weiwei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Thunström, P.
    Vienna Univ Technol, Inst Solid State Phys, A-1040 Vienna, Austria..
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Sch Informat & Commun Technol, Dept Mat & Nanophys, Electrum 229, SE-16440 Kista, Sweden.;KTH, SeRC Swedish & Sci Res Ctr, SE-10044 Stockholm, Sweden..
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Kvashnin, Yaroslav O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    van Schilfgaarde, M.
    Kings Coll London, Dept Phys, London WC2R 2LS, England..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sarma, Dipankar Das
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.;CSIR, NISE, New Delhi 110001, India..
    High photon energy spectroscopy of NiO: Experiment and theory2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 23, article id 235138Article in journal (Refereed)
    Abstract [en]

    We have revisited the valence band electronic structure of NiO by means of hard x-ray photoemission spectroscopy (HAXPES) together with theoretical calculations using both the GW method and the local density approximation + dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity problem in DMFT is solved through the exact diagonalization (ED) method. We show that the LDA+DMFT method in conjunction with the standard fully localized limit (FLL) and around mean field (AMF) double-counting alone cannot explain all the observed structures in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and p derived states to properly position their binding energies. Our results establish that a combination of the GW and DMFT methods is necessary for correctly describing the electronic structure of NiO in a proper ab initio framework. We also demonstrate that the inclusion of photoionization cross section is crucial to interpret the HAXPES spectra of NiO. We argue that our conclusions are general and that the here suggested approach is appropriate for any complex transition metal oxide.

  • 50.
    Paul, Souvik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Iusan, Diana
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, Electrum 229, SE-16440 Kista, Sweden..
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden.;KTH Royal Inst Technol, SeRC, SE-10044 Stockholm, Sweden..
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125120Article in journal (Refereed)
    Abstract [en]

    Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of BiFeO3, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the LDA+U approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe 3d states, whereas the LDA+U method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe 3d orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe 3d states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.

12 1 - 50 of 71
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