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  • 1.
    Albaalbaky, Ahmed
    et al.
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ledue, Denis
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Patte, Renaud
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Fresard, Raymond
    Normandie Univ, UNICAEN, ENSICAEN, CNRS,CRISMAT, F-14050 Caen, France..
    Magnetoelectric properties of multiferroic CuCrO2 studied by means of ab initio calculations and Monte Carlo simulations2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 6, article id 064431Article in journal (Refereed)
    Abstract [en]

    Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO2 below its Neel temperature T-N, we investigate its magnetic and ferroelectric properties using ab initio calculations and Monte Carlo simulations. Exchange interactions up to the third nearest neighbors in the ab plane, interlayer interaction, and single ion anisotropy constants in CuCrO2 are estimated by a series of density functional theory calculations. In particular, our results evidence a hard axis along the [110] direction due to the lattice distortion that takes place along this direction below T-N. Our Monte Carlo simulations indicate that the system possesses a Neel temperature T-N approximate to 27 K very close to the ones reported experimentally (T-N = 24-26 K). Also we show that the ground state is a proper-screw magnetic configuration with an incommensurate propagation vector pointing along the [110] direction. Moreover, our work reports the emergence of spin helicity below T-N which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model. We confirm the electric control of spin helicity by simulating P-E hysteresis loops at various temperatures.

  • 2.
    Beutier, G.
    et al.
    Univ Grenoble Alpes, CNRS, Grenoble INP, SIMaP, F-38000 Grenoble, France..
    Collins, S. P.
    Diamond Light Source Ltd, Diamond House,Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England..
    Dimitrova, O. V.
    Moscow MV Lomonosov State Univ, Moscow 119991, Russia..
    Dmitrienko, V. E.
    RAS, FSRC Crystallog & Photon, AV Shubnikov Inst Crystallog, Moscow 119333, Russia..
    Katsnelson, M. I.
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.;Ural Fed Univ, Dept Theoret Phys & Appl Math, Mira 19, Ekaterinburg 620002, Russia..
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lichtenstein, A. I.
    Ural Fed Univ, Dept Theoret Phys & Appl Math, Mira 19, Ekaterinburg 620002, Russia.;Univ Hamburg, Inst Theoret Phys 1, Jungiusstr 9, D-20355 Hamburg, Germany..
    Mazurenko, V. V.
    Ural Fed Univ, Dept Theoret Phys & Appl Math, Mira 19, Ekaterinburg 620002, Russia..
    Nisbet, A. G. A.
    Diamond Light Source Ltd, Diamond House,Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England..
    Ovchinnikova, E. N.
    Moscow MV Lomonosov State Univ, Moscow 119991, Russia..
    Pincini, D.
    Diamond Light Source Ltd, Diamond House,Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England.;UCL, London Ctr Nanotechnol, London WC1E 6BT, England.;UCL, Dept Phys & Astron, London WC1E 6BT, England..
    Band Filling Control of the Dzyaloshinskii-Moriya Interaction in Weakly Ferromagnetic Insulators2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 16, article id 167201Article in journal (Refereed)
    Abstract [en]

    We observe and explain theoretically a dramatic evolution of the Dzyaloshinskii-Moriya interaction (DMI) in the series of isostructural weak ferromagnets, MnCO3, FeBO3, CoCO3, and NiCO3. The sign of the interaction is encoded in the phase of the x-ray magnetic diffraction amplitude, observed through interference with resonant quadrupole scattering. We find very good quantitative agreement with first-principles electronic structure calculations, reproducing both sign and magnitude through the series, and propose a simplified "toy model" to explain the change in sign with 3d shell filling. The model gives insight into the evolution of the DMI in Mott and charge transfer insulators.

  • 3.
    Bondarenko, N.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chico, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, N. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Spin-polaron formation and magnetic state diagram in La-doped CaMnO32017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 22, article id 220401Article in journal (Refereed)
    Abstract [en]

    LaxCa1-xMnO3 (LCMO) has been studied in the framework of density functional theory (DFT) using Hubbard-U correction. We show that the formation of spin polarons of different configurations is possible in the G-type antiferromagnetic phase. We also show that the spin-polaron (SP) solutions are stabilized due to an interplay of magnetic and lattice effects at lower La concentrations and mostly due to the lattice contribution at larger concentrations. Our results indicate that the development of SPs is unfavorable in the C- and A-type antiferromagnetic phases. The theoretically obtained magnetic state diagram is in good agreement with previously reported experimental results.

  • 4.
    Cardias, R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Fed Univ Para, Fac Fis, Belem, PA, Brazil.
    Szilva, Attila
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    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.
    Katsnelson, M. I.
    Radboud Univ Nijmegen, Inst Mol & Mat, Heijendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.;Ural Fed Univ, Theoret Phys & Appl Math Dept, Mira Str 19, Ekaterinburg 620002, Russia..
    Lichtenstein, A. I.
    Ural Fed Univ, Theoret Phys & Appl Math Dept, Mira Str 19, Ekaterinburg 620002, Russia.;Univ Hamburg, Inst Theoret Phys, Jungiusstrasse 9, D-20355 Hamburg, Germany..
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Klautau, A. B.
    Fed Univ Para, Fac Fis, Belem, PA, Brazil..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    The Bethe-Slater curve revisited; new insights from electronic structure theory2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 4058Article in journal (Refereed)
    Abstract [en]

    The Bethe-Slater (BS) curve describes the relation between the exchange coupling and interatomic distance. Based on a simple argument of orbital overlaps, it successfully predicts the transition from antiferromagnetism to ferromagnetism, when traversing the 3d series. In a previous article [Phys. Rev. Lett. 116, 217202 (2016)] we reported that the dominant nearestneighbour (NN) interaction for 3d metals in the bcc structure indeed follows the BS curve, but the trends through the series showed a richer underlying physics than was initially assumed. The orbital decomposition of the inter-site exchange couplings revealed that various orbitals contribute to the exchange interactions in a highly non-trivial and sometimes competitive way. In this communication we perform a deeper analysis by comparing 3d metals in the bcc and fcc structures. We find that there is no coupling between the E-g orbitals of one atom and T-2g orbitals of its NNs, for both cubic phases. We demonstrate that these couplings are forbidden by symmetry and formulate a general rule allowing to predict when a similar situation is going to happen. In gamma-Fe, as in alpha-Fe, we find a strong competition in the symmetry-resolved orbital contributions and analyse the differences between the high-spin and low-spin solutions.

  • 5.
    Cardias, Ramon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bezerra-Neto, M. M.
    Instituto de Engenharia e Geociências, Universidade Federal do Oeste do Pará, Santarém, PA, Brazil.
    Ribeiro, M. S.
    Instituto Federal do Pará, Campus Belém, PA, Brazil.
    Szilva, Attila
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    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.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Klautau, A. B.
    Faculdade de Física, Universidade Federal do Pará, Belém, Pará, Brazil.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    First-principles Dzyaloshinskii-Moryia interaction in a non-collinear frameworkManuscript (preprint) (Other academic)
    Abstract [en]

    Including dierent terms in the spin-Hamiltonian, we have derived an expression for theDzyaloshinskii-Moryia vector interaction (DMI) where all the three components of the vector canbe calculated independently of the magnetic conguration. Here, we have chosen the Cr triangulartrimer on Au(111) and Mn triangular trimes on Ag(111) and Au(111) surfaces to study the implementationof the derived DMI into the RS-LMTO-ASA method. Our results have shown thatthe DMI value (module and direction) is drastically dierent for collinear and non-collinear states.Based on relation between the spin and charge currents owing in the system and the non-collinearmagnetic conguration of the triangular trimer, we argued that the drastic change between the DMIcalculated considering a collinear and a non-collinear magnetic conguration can be explained bythe mechanism behind the spin and charge currents owing through the atoms when the spins arealigned in a non-collinear fashion.

  • 6.
    Chico, Jonathan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Keshavarz, Samara
    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.
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Etz, Corina
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, Lars
    First principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys2016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 93, no 21, article id 214439Article in journal (Refereed)
    Abstract [en]

    Heusler alloys have been intensively studied due to the wide variety of properties that they exhibit. One of these properties is of particular interest for technological applications, i.e., the fact that some Heusler alloys are half-metallic. In the following, a systematic study of the magnetic properties of three different Heusler families Co(2)MnZ, Co(2)FeZ, and Mn(2)VZ with Z = (Al, Si, Ga, Ge) is performed. A key aspect is the determination of the Gilbert damping from first-principles calculations, with special focus on the role played by different approximations, the effect that substitutional disorder and temperature effects. Heisenberg exchange interactions and critical temperature for the alloys are also calculated as well as magnon dispersion relations for representative systems, the ferromagnetic Co2FeSi and the ferrimagnetic Mn2VAl. Correlation effects beyond standard density-functional theory are treated using both the local spin density approximation including the Hubbard U and the local spin density approximation plus dynamical mean field theory approximation, which allows one to determine if dynamical self-energy corrections can remedy some of the inconsistencies which were previously reported for these alloys.

  • 7.
    Chimata, Raghuveer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Szilva, Attila
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cardias, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Fed Para, Fac Fis, Belem, PA, Brazil.
    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.
    Mankovsky, S
    Univ Munich, Dept Chem, Butenandtstr 5-13, D-81377 Munich, Germany.
    Ebert, H
    Univ Munich, Dept Chem, Butenandtstr 5-13, D-81377 Munich, Germany.
    Thonig, Danny
    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.
    Klautau, A. B
    Univ Fed Para, Fac Fis, Belem, PA, Brazil.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature2017In: Physical review B, ISSN 2469-9950, Vol. 95, no 21, article id 214417Article in journal (Refereed)
    Abstract [en]

    Temperature-dependent magnetic experiments such as pump-probe measurements generated by a pulsed laser have become a crucial technique for switching the magnetization in the picosecond time scale. Apart from having practical implications on the magnetic storage technology, the research field of ultrafast magnetization poses also fundamental physical questions. To correctly describe the time evolution of the atomic magnetic moments under the influence of a temperature-dependent laser pulse, it remains crucial to know if the magnetic material under investigation has magnetic excitation spectrum that is more or less dependent on the magnetic configuration, e.g., as reflected by the temperature dependence of the exchange interactions. In this paper, we demonstrate from first-principles theory that the magnetic excitation spectra in Co in fcc, bcc, and hcp structures are nearly identical in a wide range of noncollinear magnetic configurations. This is a curious result of a balance between the size of the magnetic moments and the strength of the Heisenberg exchange interactions, that in themselves vary with configuration, but put together in an effective spin Hamiltonian results in a configuration-independent effective model. We have used such a Hamiltonian, together with ab initio calculated damping parameters, to investigate the magnon dispersion relationship as well as ultrafast magnetization dynamics of Co and Co-rich CoMn alloys.

  • 8.
    Delczeg-Czirjak, Erna K.
    et al.
    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.
    Bergqvist, L.
    Kvashnin, Yaroslav O.
    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.
    Li, Guijiang
    Vitos, Levente
    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.
    Origin of the magnetostructural coupling in FeMnP0.75Si0.252014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 21, p. 214436-Article in journal (Refereed)
    Abstract [en]

    The strong coupling between the crystal structure and magnetic state (ferromagnetic or helical antiferromagnetic) of FeMnP0.75Si0.25 is investigated using density functional theory in combination with atomistic spin dynamics. We find many competing energy minima for drastically different ferromagnetic and noncollinear magnetic configurations. We also find that the appearance of a helical spin-spiral magnetic structure at finite temperature is strongly related to one of the crystal structures reported for this material. Shorter Fe-Fe distances are found to lead to a destabilized ferromagnetic coupling, while out-of-plane Mn-Mn exchange interactions become negative with the shortening of the interatomic distances along the c axis, implying an antiferromagnetic coupling for the nearest-neighbor Mn-Mn interactions. The impact of the local dynamical correlations is also discussed.

  • 9.
    Di Marco, Igor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Held, Andreas
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Keshavarz, Samara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chioncel, Liviu
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany..
    Half-metallicity and magnetism in the Co2MnAl/CoMnVAl heterostructure2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 3, article id 035105Article in journal (Refereed)
    Abstract [en]

    We present a study of the electronic structure and magnetism of Co2MnAl, CoMnVAl, and their heterostructure. We employ a combination of density-functional theory and dynamical mean-field theory (DFT+DMFT). We find that Co2MnAl is a half-metallic ferromagnet, whose electronic and magnetic properties are not drastically changed by strong electronic correlations, static or dynamic. Nonquasiparticle states are shown to appear in the minority spin gap without affecting the spin polarization at the Fermi level predicted by standard DFT. We find that CoMnVAl is a semiconductor or a semimetal, depending on the employed computational approach. We then focus on the electronic and magnetic properties of the Co2MnAl/CoMnVAl heterostructure, predicted by previous first-principle calculations as a possible candidate for spin-injecting devices. We find that two interfaces, Co-Co/V-Al and Co-Mn/Mn-Al, preserve the half-metallic character, with and without including electronic correlations. We also analyze the magnetic exchange interactions in the bulk and at the interfaces. At the Co-Mn/Mn-Al interface, competing magnetic interactions are likely to favor the formation of a noncollinear magnetic order, which is detrimental for the spin polarization.

  • 10.
    Ivanov, Sergey A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Karpov Inst Phys Chem, Ctr Mat Sci, Vorontsovo Pole 10, Moscow 105064, Russia..
    Bush, A. A.
    Moscow State Univ Informat Technol RadioEngn & El, Pr Ventadskogo 78, Moscow 119454, Russia..
    Ritter, C.
    Inst Laue Langevin, BP 156, F-38042 Grenoble, France..
    Behtin, M. A.
    Moscow State Univ Informat Technol RadioEngn & El, Pr Ventadskogo 78, Moscow 119454, Russia..
    Cherepanov, V. M.
    Kurchatov Inst, Natl Res Ctr, Pl Kurchatova 1, Moscow 123182, Russia..
    Autieri, Carmine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O.
    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.
    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.
    Kumar, P. Anil
    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.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Evolution of the structural and multiferroic properties of PbFe2/3W1/3O3 ceramics upon Mn-doping2017In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 187, p. 218-232Article in journal (Refereed)
    Abstract [en]

    The perovskite system Pb(Fe1-xMnx)(2/3)W1/3O3 (0 <= x <= 1, PFMWO) has been prepared by conventional solid-state reaction under different sintering conditions. Structures and phase composition as well as thermal, magnetic and dielectric properties of the compounds have been systematically investigated experimentally and by first-principles density functional calculations. A clean perovskite phase is established at room temperature for compositions 0 <= x <= 0.4. Rietveld refinements of X-ray and neutron powder diffraction patterns demonstrate that the compounds crystallize in space group Pm-3m (0 <= x <= 0.4). The degree of ordering of the Fe and W/Mn cations was found to depend on the concentration of Mn. First-principles calculations suggest that the structural properties of PFMWO are strongly influenced by the Jahn Teller effect. The PFMWO compounds behave as relaxor ferroelectrics at weak Mn-doping with a dielectric constant that rapidly decreases with increasing Mn content. A low temperature antiferromagnetic G-type order with propagation vector k = (1/2,1/2,1/2) is derived from neutron powder diffraction data for the samples with x <= 0.4. However with increasing doping concentration, the magnetic order is perturbed. First principles calculations show that the dominant exchange coupling is antiferromagnetic and occurs between nearest neighbor Fe atoms. When the system is doped with Mn, a relatively weak ferromagnetic (FM) interaction between Fe and Mn atoms emerges. However, due to the presence of this FM interaction, the correlation length of the magnetic order is greatly shortened already at rather low doping levels.

  • 11.
    Ivanov, Sergey A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Karpov Inst Phys Chem, Ctr Mat Sci, Vorontsovo Pole 10,K-64, Moscow 105064, Russia.
    Bush, Alexander A
    Moscow State Inst Radio Engn Elect & Automat, RU-119434 Moscow, Russia.
    Stash, Adam I
    Karpov Inst Phys Chem, Ctr Mat Sci, Vorontsovo Pole 10,K-64, Moscow 105064, Russia.
    Kamentsev, Konstantin E
    Moscow State Inst Radio Engn Elect & Automat, RU-119434 Moscow, Russia.
    Shkuratov, Valerii Ya
    Moscow State Inst Radio Engn Elect & Automat, RU-119434 Moscow, Russia.
    Kvashnin, Yaroslav O
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Autieri, Carmine
    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.
    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.
    Nordblad, Per
    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.
    Polar Order and Frustrated Antiferromagnetism in Perovskite Pb2MnWO6 Single Crystals.2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 6, p. 2791-2805Article in journal (Refereed)
    Abstract [en]

    Single crystals of the multiferroic double-perovskite Pb2MnWO6 have been synthesized and their structural, thermal, magnetic and dielectric properties studied in detail. Pure perovskite-phase formation and stoichiometric chemical composition of the as-grown crystals are confirmed by X-ray single-crystal and powder diffraction techniques as well as energy-dispersive X-ray and inductively coupled plasma mass spectrometry. Detailed structural analyses reveal that the crystals experience a structural phase transition from the cubic space group (s.g.) Fm3̅m to an orthorhombic structure in s.g. Pn21a at about 460 K. Dielectric data suggest that a ferrielectric phase transition takes place at that same temperature, in contrast to earlier results on polycrystalline samples, which reported a transition to s.g. Pnma and an antiferroelectric low-temperature phase. Magnetic susceptibility measurements indicate that a frustrated antiferromagnetic phase emerges below 8 K. Density functional theory based calculations confirm that the cationic order between Mn and W is favorable. The lowest total energy was found for an antiferromagnetically ordered state. However, analyses of the calculated exchange parameters revealed strongly competing antiferromagnetic interactions. The large distance between the magnetic atoms, together with magnetic frustration, is shown to be the main reason for the low value of the ordering temperature observed experimentally. We discuss the structure-property relationships in Pb2MnWO6 and compare these observations to reported results on related Pb2BWO6 perovskites with different B cations.

  • 12.
    Keshavarz, Samara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kontos, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wardecki, Dariusz
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden;Univ Warsaw, Fac Phys, Inst Expt Phys, Pasteura 5, PL-02093 Warsaw, Poland;Chalmers Univ Technol, Dept Chem & Chem Engn, SE-41296 Gothenburg, Sweden.
    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.
    Panda, Swarup K.
    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.
    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.
    Grins, Jekabs
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.
    Svensson, Gunnar
    Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.
    Gunnarsson, Klas
    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.
    Magnetic properties of Ruddlesden-Popper phases Sr3-&: A combined experimental and theoretical investigation2018In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 4, article id 044005Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive study of the magnetic properties of Sr3-xYx(Fe1.25Ni0.75)O-7(-delta )(0 <= x <= 0.75). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by a theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the Ned temperature (T-N) with an increase of Y concentrations and O occupancy. The NPD data reveal that all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the three-dimensional magnetic order is stabilized due to finite interlayer exchange couplings. The latter give rise to finite interlayer spin-spin correlations, which disappear above T-N.

  • 13.
    Keshavarz, Samara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O.
    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.
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat & Nano Phys, SE-16440 Kista, Sweden..
    Katsnelson, M. I.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands.;Ural Fed Univ, Dept Appl Math & Theoret Phys, Ekaterinburg 620002, Russia..
    Lichtenstein, A. I.
    Ural Fed Univ, Dept Appl Math & Theoret Phys, Ekaterinburg 620002, Russia.;Univ Hamburg, Inst Theoret Phys, D-20355 Hamburg, Germany..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Layer-resolved magnetic exchange interactions of surfaces of late 3d elements: Effects of electronic correlations2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 16, article id 165129Article in journal (Refereed)
    Abstract [en]

    We present the results of an ab initio study of the magnetic properties of Fe, Co, and Ni surfaces. In particular, we discuss their electronic structure and magnetic exchange interactions (J(ij)), as obtained bymeans of a combination of density functional theory and dynamical mean-field theory. All studied systems have a pronounced tendency to ferromagnetism both for bulk and surface atoms. The presence of narrowband surface states is shown to enhance the magnetic moment as well as the exchange couplings. The most interesting results were obtained for the Fe surface where the atoms have a tendency to couple antiferromagnetically with each other. This interaction is relatively small when compared to interlayer ferromagnetic interaction, and it depends strongly on the lattice parameter. Local correlation effects are shown to lead to strong changes of the overall shape of the spectral functions. However, they seem not to play a decisive role in the overall picture of magnetic couplings studied here. We have also investigated the influence of correlations on the spin and orbital moments of bulklike and surface atoms. We found that dynamical correlations in general lead to enhanced values of the orbital moment.

  • 14.
    Keshavarz, Samara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rodrigues, Debora C. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Fed Univ Para, Fac Fis, BR-66075110 Belem, Para, Brazil..
    Pereiro, Manuel
    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.
    Autieri, Carmine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Solovyev, I. V.
    atl Inst Mat Sci, 1-1 Namiki, Tsukuba, Ibaraki 3050044, Japan.; Ural Fed Univ, Dept Theoret Phys & Appl Math, Mira St 19, Ekaterinburg 620002, Russia..
    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.
    Exchange interactions of CaMnO3 in the bulk and at the surface2017In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 95, article id 115120Article in journal (Refereed)
    Abstract [en]

    We present electronic and magnetic properties of CaMnO3 (CMO) as obtained from ab initio calculations. We identify the preferable magnetic order by means of density functional theory plus Hubbard U calculations and extract the effective exchange parameters (Jij ' s) using the magnetic force theorem. We find that the effects of geometrical relaxation at the surface as well as the change of crystal field are very strong and are able to influence the lower-energymagnetic configuration. In particular, our analysis reveals that the exchange interaction between the Mn atoms belonging to the surface and the subsurface layers is very sensitive to the structural changes. An earlier study [A. Filippetti and W. E. Pickett, Phys. Rev. Lett. 83, 4184 (1999)] suggested that this coupling is ferromagnetic and gives rise to the spin-flip (SF) process on the surface of CMO. In our work, we confirm their finding for an unrelaxed geometry, but once the structural relaxations are taken into account, this exchange coupling changes its sign. Thus, we suggest that the surface of CMO should have the same G-type antiferromagnetic order as in the bulk. Finally, we show that the suggested SF can be induced in the system by introducing an excess of electrons.

  • 15.
    Keshavarz, Samara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Millis, Andrew J.
    Columbia Univ, Dept Phys, New York, NY USA; Flatiron Inst, Ctr Computat Quantum Phys, New York, NY USA.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic structure, magnetism, and exchange integrals in transition-metal oxides: Role of the spin polarization of the functional in DFT+U calculations2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 18, article id 184404Article in journal (Refereed)
    Abstract [en]

    Density functional theory augmented with Hubbard-U corrections (DFT+U) is currently one of the most widely used methods for first-principles electronic structure modeling of insulating transition-metal oxides (TMOs). Since U is relatively large compared to bandwidths, the magnetic excitations in TMOs are expected to be well described by a Heisenberg model. However, in practice the calculated exchange parameters J(ij) depend on the magnetic configuration from which they are extracted and on the functional used to compute them. In this work we investigate how the spin polarization dependence of the underlying exchange-correlation functional influences the calculated magnetic exchange constants of TMOs. We perform a systematic study of the predictions of calculations based on the local density approximation plus U (LDA+U) and the local spin density approximation plus U (LSDA+U) for the electronic structures, total energies, and magnetic exchange interactions Jij extracted from ferromagnetic (FM) and antiferromagnetic (AFM) configurations of several transition-metal oxide materials. We report that for realistic choices of Hubbard U and Hund's J parameters, LSDA+U and LDA+U calculations result in different values of the magnetic exchange constants and band gap. The dependence of the band gap on the magnetic configuration is stronger in LDA+U than in LSDA+U and we argue that this is the main reason why the configuration dependence of Jij is found to be systematically more pronounced in LDA+U than in LSDA+U calculations. We report a very good correspondence between the computed total energies and the parametrized Heisenberg model for LDA+U calculations, but not for LSDA+U, suggesting that LDA+U is a more appropriate method for estimating exchange interactions.

  • 16.
    Kvashnin, Yaroslav O.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cardias, R.
    Fed Univ Para, Fac Fis, BR-66075110 Belem, Para, Brazil..
    Szilva, Attila
    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.
    Katsnelson, M. I.
    Radboud Univ Nijmegen, Inst Mol & Mat, Heijendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.;Ural Fed Univ, Theoret Phys & Appl Math Dept, Mira St 19, Ekaterinburg 620002, Russia..
    Lichtenstein, A. I.
    Ural Fed Univ, Theoret Phys & Appl Math Dept, Mira St 19, Ekaterinburg 620002, Russia.;Univ Hamburg, Inst Theoret Phys, Jungiusstr 9, D-20355 Hamburg, Germany..
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Klautau, A. B.
    Fed Univ Para, Fac Fis, BR-66075110 Belem, Para, Brazil..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Microscopic Origin of Heisenberg and Non-Heisenberg Exchange Interactions in Ferromagnetic bcc Fe2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, no 21, article id 217202Article in journal (Refereed)
    Abstract [en]

    By means of first principles calculations, we investigate the nature of exchange coupling in ferromagnetic bcc Fe on a microscopic level. Analyzing the basic electronic structure reveals a drastic difference between the 3d orbitals of E-g and T-2g symmetries. The latter ones define the shape of the Fermi surface, while the former ones form weakly interacting impurity levels. We demonstrate that, as a result of this, in Fe the T-2g orbitals participate in exchange interactions, which are only weakly dependent on the configuration of the spin moments and thus can be classified as Heisenberg-like. These couplings are shown to be driven by Fermi surface nesting. In contrast, for the E-g states, the Heisenberg picture breaks down since the corresponding contribution to the exchange interactions is shown to strongly depend on the reference state they are extracted from. Our analysis of the nearest-neighbor coupling indicates that the interactions among E-g states are mainly proportional to the corresponding hopping integral and thus can be attributed to be of double-exchange origin. By making a comparison to other magnetic transition metals, we put the results of bcc Fe into context and argue that iron has a unique behavior when it comes to magnetic exchange interactions.

  • 17.
    Kvashnin, Yaroslav O.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grånäs, Oscar
    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.
    Katsnelson, M. I.
    Lichtenstein, A. I.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Exchange parameters of strongly correlated materials: Extraction from spin-polarized density functional theory plus dynamical mean-field theory2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 12, article id 125133Article in journal (Refereed)
    Abstract [en]

    In this paper we present an accurate numerical scheme for extracting interatomic exchange parameters (J(ij)) of strongly correlated systems, based on first-principles full-potential electronic structure theory. The electronic structure is modeled with the help of a full-potential linear muffin-tin orbital method. The effects of strong electron correlations are considered within the charge self-consistent density functional theory plus dynamical mean-field theory. The exchange parameters are then extracted using the magnetic force theorem; hence all the calculations are performed within a single computational framework. The method allows us to investigate how the Jij parameters are affected by dynamical electron correlations. In addition to describing the formalism and details of the implementation, we also present magnetic properties of a few commonly discussed systems, characterized by different degrees of electron localization. In bcc Fe, treated as a moderately correlated metal, we found a minor renormalization of the Jij interactions once the dynamical correlations are introduced. However, generally, if the magnetic coupling has several competing contributions from different orbitals, the redistribution of the spectral weight and changes in the exchange splitting of these states can lead to a dramatic modification of the total interaction parameter. In NiO we found that both static and dynamical mean-field results provide an adequate description of the exchange interactions, which is somewhat surprising given the fact that these two methods result in quite different electronic structures. By employing the Hubbard-I approximation for the treatment of the 4f states in hcp Gd we reproduce the experimentally observed multiplet structure. The calculated exchange parameters result in being rather close to the ones obtained by treating the 4f electrons as noninteracting core states.

  • 18.
    Kvashnin, Yaroslav O.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Weiwei, Sun
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic topological transition and noncollinear magnetism in compressed hcp Co2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 13, article id 134422Article in journal (Refereed)
    Abstract [en]

    Recent experiments showed that Co undergoes a phase transition from the ferromagnetic hcp phase to the nonmagnetic fcc one around 100 GPa. Since the transition is of first order, a certain region of coexistence of the two phases is present. By means of ab initio calculations, we found that the hcp phase itself undergoes a series of electronic topological transitions (ETTs), which affects both elastic and magnetic properties of the material. Most importantly, we propose that the sequence of ETTs lead to the stabilization of a noncollinear spin arrangement in highly compressed hcp Co. Details of this noncollinear magnetic state and the interatomic exchange parameters that are connected to it are presented here.

  • 19. Kvashnina, K. O.
    et al.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Butorin, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Role of resonant inelastic X-ray scattering in high-resolution core-level spectroscopy of actinide materials2014In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 194, p. 27-36Article in journal (Refereed)
    Abstract [en]

    This paper provides a brief overview of applications of advanced X-ray spectroscopic techniques that take advantage of the resonant inelastic X-ray scattering (RIXS) in the hard and tender X-ray range and have recently become available for studying the electronic structure of actinides. We focus here on the high-energy-resolution X-ray absorption near edge structure (XANES) and core-to-core and core-to-valence RIXS spectroscopies at the U L and M edges of uranium compounds. The spectral features are analyzed using a number of theoretical methods, such as the Anderson impurity model, density functional theory in the local density approximation with an added Coulomb interaction (LDA + U), and full multiple scattering (FEFF) and ab initio finite difference method near-edge structure (FDMNES) codes. In connection with presented results, the capabilities and limitations of the experimental techniques and theoretical methods are discussed. (C) 2014 Elsevier B.V. All rights reserved.

  • 20.
    Kvashnina, Kristina
    et al.
    European Synchrotron Radiat Facil, F-38043 Grenoble, France..
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. European Synchrotron Radiat Facil, F-38043 Grenoble, France..
    Vegelius, Johan R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Bosak, Alexei
    European Synchrotron Radiat Facil, F-38043 Grenoble, France..
    Martin, Philippe M.
    CEN Cadarache, CEA, DEC, DEN, F-13108 St Paul Les Durance, France..
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sensitivity to Actinide Doping of Uranium Compounds by Resonant Inelastic X-ray Scattering at Uranium L-3 Edge2015In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 87, no 17, p. 8772-8780Article in journal (Refereed)
    Abstract [en]

    Valence-to-core resonant inelastic X-ray scattering (RIXS) and high energy resolution fluorescence detection (HERFD) X-ray absorption measurements were performed at the U (L)3 edges of UO2 and UO2(NO3)(2)(H2O)(6). The results are compared with model calculations based on the local-density-approximation formalism, taking into account Coulomb interaction U (LDA + U). We show that despite strong 5f-5f electronic correlations in the studied systems and the use of core-level excitations in the intermediate stage of the spectroscopic process, the RIXS technique probes a convolution of the single-particle densities of states in the valence and conduction bands. For UO2, the detected crystal-field splitting between the U 6d e(g) and t(2g) orbitals from the RIXS spectra (similar to 3.5 eV) is larger than that previously derived from optical spectroscopy. Furthermore, by using an example of the U0.75Pu0.25O2 mixed oxide, we show that the RIXS technique at the U L-3 edges is sensitive to the substitution of U with other actinide, in contrast to conventional X-ray absorption methods. That is, due to changes in the occupied part rather than in the unoccupied part of the U 6d states caused by the substitution.

  • 21. Lejaeghere, Kurt
    et al.
    Bihlmayer, Gustav
    Björkman, Torbjörn
    Blaha, Peter
    Blügel, Stefan
    Blum, Volker
    Caliste, Damien
    Castelli, Ivano E
    Clark, Stewart J
    Dal Corso, Andrea
    de Gironcoli, Stefano
    Deutsch, Thierry
    Dewhurst, John Kay
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Draxl, Claudia
    Dułak, Marcin
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Flores-Livas, José A
    Garrity, Kevin F
    Genovese, Luigi
    Giannozzi, Paolo
    Giantomassi, Matteo
    Goedecker, Stefan
    Gonze, Xavier
    Grånäs, Oscar
    Gross, E K U
    Gulans, Andris
    Gygi, François
    Hamann, D R
    Hasnip, Phil J
    Holzwarth, N A W
    Iuşan, Diana
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jochym, Dominik B
    Jollet, François
    Jones, Daniel
    Kresse, Georg
    Koepernik, Klaus
    Küçükbenli, Emine
    Kvashnin, Yaroslav O
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Locht, Inka L M
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lubeck, Sven
    Marsman, Martijn
    Marzari, Nicola
    Nitzsche, Ulrike
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ozaki, Taisuke
    Paulatto, Lorenzo
    Pickard, Chris J
    Poelmans, Ward
    Probert, Matt I J
    Refson, Keith
    Richter, Manuel
    Rignanese, Gian-Marco
    Saha, Santanu
    Scheffler, Matthias
    Schlipf, Martin
    Schwarz, Karlheinz
    Sharma, Sangeeta
    Tavazza, Francesca
    Thunström, Patrik
    Tkatchenko, Alexandre
    Torrent, Marc
    Vanderbilt, David
    van Setten, Michiel J
    Van Speybroeck, Veronique
    Wills, John M
    Yates, Jonathan R
    Zhang, Guo-Xu
    Cottenier, Stefaan
    Reproducibility in density functional theory calculations of solids.2016In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 351, no 6280, p. 1415-1422Article in journal (Refereed)
    Abstract [en]

    The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We report the results of a community-wide effort that compared 15 solid-state codes, using 40 different potentials or basis set types, to assess the quality of the Perdew-Burke-Ernzerhof equations of state for 71 elemental crystals. We conclude that predictions from recent codes and pseudopotentials agree very well, with pairwise differences that are comparable to those between different high-precision experiments. Older methods, however, have less precise agreement. Our benchmark provides a framework for users and developers to document the precision of new applications and methodological improvements.

  • 22. Li, Guijiang
    et al.
    Li, Wei
    Schonecker, Stephan
    Li, Xiaoqing
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O.
    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.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kinetic arrest induced antiferromagnetic order in hexagonal FeMnP0.75Si0.25 alloy2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 26, p. 262405-Article in journal (Refereed)
    Abstract [en]

    The magnetic state of the FeMnP0.75Si0.25 alloy was investigated by first principles calculations. The coexistence of ferromagnetic and antiferromagnetic phases in FeMnP0.75Si0.25 with the same hexagonal crystal structure was revealed. It was found that kinetic arrest during the transition from the high temperature disordered paramagnetic phase to the low temperature ordered ferromagnetic phase results in the intermediate metastable and partially disordered antiferromagnetic phase. We propose that the ratio of the ferromagnetic and antiferromagnetic phases in the FeMnP0.75Si0.25 sample can be tuned by adjusting the kinetic process of atomic diffusion. The investigations suggest that careful control of the kinetic diffusion process provides another tuning parameter to design candidate magnetocaloric materials. (C) 2014 AIP Publishing LLC.

  • 23.
    Locht, Inka L. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rodrigues, Debora C. M.
    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.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, L.
    Katsnelson, M. I.
    Delin, Anna
    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.
    The standard model of the rare-earths, analyzed from the Hubbard-IapproximationManuscript (preprint) (Other academic)
  • 24.
    Lüder, Johann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. National University of Singapore, Department of Mechanical Engineering.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Haverkort, Maurits W.
    Heidelberg University, Institute for Theoretical Physics.
    Thunström, Patrik
    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. Örebro University, School of Science and Technology.
    Sanyal, Biplab
    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.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theory of L-edge spectroscopy of strongly correlated systems2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, article id 245131Article in journal (Refereed)
    Abstract [en]

    X-ray absorption spectroscopy measured at the L edge of transition metals (TMs) is a powerful element-selective tool providing direct information about the correlation effects in the 3d states. The theoretical modeling of the 2p→3d excitation processes remains to be challenging for contemporary ab initio electronic structure techniques, due to strong core-hole and multiplet effects influencing the spectra. In this work, we present a realization of the method combining the density-functional theory with multiplet ligand field theory, proposed in Haverkort et al. [Phys. Rev. B 85, 165113 (2012)]. In this approach, a single-impurity Anderson model (SIAM) is constructed, with almost all parameters obtained from first principles, and then solved to obtain the spectra. In our implementation, we adopt the language of the dynamical mean-field theory and utilize the local density of states and the hybridization function, projected onto TM 3d states, in order to construct the SIAM. The developed computational scheme is applied to calculate the L-edge spectra for several TM monoxides. A very good agreement between the theory and experiment is found for all studied systems. The effect of core-hole relaxation, hybridization discretization, possible extensions of the method as well as its limitations are discussed.

  • 25. Mazurenko, V. V.
    et al.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jin, Fengping
    De Raedt, H. A.
    Lichtenstein, A. I.
    Katsnelson, M. I.
    First-principles modeling of magnetic excitations in Mn-122014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 21, p. 214422-Article in journal (Refereed)
    Abstract [en]

    We have developed a fully microscopic theory of magnetic properties of the prototype molecular magnet Mn-12. First, the intramolecular magnetic properties have been studied by means of first-principles density functional based methods, with local correlation effects being taken into account within the local density approximation plus U (LDA + U) approach. Using the magnetic force theorem, we have calculated the interatomic isotropic and anisotropic exchange interactions and full tensors of single-ion anisotropy for each Mn ion. Dzyaloshinskii-Moriya (DM) interaction parameters turned out to be unusually large, reflecting a low symmetry of magnetic pairs in molecules, in comparison with bulk crystals. Based on these results we predict a distortion of ferrimagnetic ordering due to DM interactions. Further, we use an exact diagonalization approach allowing one to work with as large a Hilbert space dimension as 108 without any particular symmetry (the case of the constructed magnetic model). Based on the computational results for the excitation spectrum, we propose a distinct interpretation of the experimental inelastic neutron scattering spectra.

  • 26.
    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.

  • 27.
    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.

  • 28.
    Shaw, Justin M.
    et al.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Delczeg-Czirjak, Erna K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edwards, Eric R. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Kvashnin, Yaroslav
    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.
    Schoen, Martin A. W.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.;Univ Regensburg, Dept Phys, Regensburg, Germany..
    Pufall, Matt
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Schneider, Michael L.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Silva, Thomas J.
    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.
    Rice, Katherine P.
    CAMECA Instruments, Madison, WI 53711 USA..
    Olle, Eriksson
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, Örebro, Sweden..
    Nembach, Hans T.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA..
    Magnetic damping in sputter-deposited Co2MnGe Heusler compounds with A2, B2, and L2(1) orders: Experiment and theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094420Article in journal (Refereed)
    Abstract [en]

    We show that very low values of the magnetic damping parameter can be achieved in sputter deposited polycrystalline films of Co2MnGe annealed at relatively low temperatures ranging from 240 degrees C to 400 degrees C. Damping values as low as 0.0014 are obtained with an intrinsic value of 0.0010 after spin-pumping contributions are considered. Of importance to most applications is the low value of inhomogeneous linewidth that yields measured linewidths of 1.8 and 5.1 mT at 10 and 40 GHz, respectively. The damping parameter monotonically decreases as the B2 order of the films increases. This trend is reproduced and explained by ab initio calculations of the electronic structure and damping parameter. Here, the damping parameter is calculated as the structure evolves from A2 to B2 to L2(1) orders. The largest decrease in the damping parameter occurs during the A2 to B2 transition as the half-metallic phase becomes established.

  • 29.
    Szilva, Attila
    et al.
    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.
    Bessarab, P. F.
    Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;ITMO Univ, Dept Nanophoton & Metamat, St Petersburg 197101, Russia..
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rodrigues, Debora C. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Fed Para, Fac Fis, BR-66075110 Belem, Para, Brazil..
    Cardias, R.
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, A.
    Univ Versailles, Univ Paris Sud, CEA, CNRS,INRIA,Maison Simulat,USR 3441, F-91191 Gif Sur Yvette, France.;CEA, INAC MEM, F-38000 Grenoble, France..
    Klautau, A. B.
    Univ Fed Para, Fac Fis, BR-66075110 Belem, Para, Brazil..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theory of noncollinear interactions beyond Heisenberg exchange: Applications to bcc Fe2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 14, article id 144413Article in journal (Refereed)
    Abstract [en]

    We show for a simple noncollinear configuration of the atomistic spins (in particular, where one spin is rotated by a finite angle in a ferromagnetic background) that the pairwise energy variation computed in terms of multiple-scattering formalism cannot be fully mapped onto a bilinear Heisenberg spin model even in the absence of spin-orbit coupling. The non-Heisenberg terms induced by the spin-polarized host appear in leading orders in the expansion of the infinitesimal angle variations. However, an E-g - T-2g symmetry analysis based on the orbital decomposition of the exchange parameters in bcc Fe leads to the conclusion that the nearest-neighbor exchange parameters related to the T-2g orbitals are essentially Heisenberg-like: they do not depend on the spin configuration, and can, in this case, be mapped onto a Heisenberg spin model even in extreme noncollinear cases.

  • 30.
    Söderlind, P.
    et al.
    Lawrence Livermore Natl Lab, Dept Phys, Livermore, CA 94551 USA..
    Landa, A.
    Lawrence Livermore Natl Lab, Dept Phys, Livermore, CA 94551 USA..
    Locht, Inka L. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Åberg, D.
    Lawrence Livermore Natl Lab, Dept Phys, Livermore, CA 94551 USA..
    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.
    Dane, M.
    Lawrence Livermore Natl Lab, Dept Phys, Livermore, CA 94551 USA..
    Turchi, P. E. A.
    Lawrence Livermore Natl Lab, Dept Phys, Livermore, CA 94551 USA..
    Antropov, V. P.
    Ames Lab, Div Mat Sci & Engn, Ames, IA 50011 USA..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Prediction of the new efficient permanent magnet SmCoNiFe32017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 10, article id 100404Article in journal (Refereed)
    Abstract [en]

    We propose a new efficient permanent magnet, SmCoNiFe3, which is a development of the well-known SmCo5 prototype. More modern neodymium magnets of the Nd-Fe-B type have an advantage over SmCo5 because of their greater maximum energy products due to their iron-rich stoichiometry. Our new magnet, however, removes most of this disadvantage of SmCo5 while preserving its superior high-temperature efficiency over the neodymium magnets. We show by means of first-principles electronic-structure calculations that SmCoNiFe3 has very favorable magnetic properties and could therefore potentially replace SmCo5 or Nd-Fe-B types in various applications.

  • 31.
    Thersleff, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Stockholm Univ, MMK, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden..
    Muto, Shunsuke
    Nagoya Univ, Adv Measurement Technol Ctr, Inst Mat & Syst Sustainabil, Chikusa Ku, Nagoya, Aichi 4648603, Japan..
    Werwinski, Miroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Polish Acad Sci, Inst Mol Phys, M Smoluchowskiego 17, PL-60179 Poznan, Poland..
    Spiegelberg, Jakob
    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.
    Hjörvarsson, Björgvin
    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.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 44802Article in journal (Refereed)
    Abstract [en]

    While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution.

  • 32.
    Thonig, Danny
    et al.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro University, School of Science & Technology, Örebro, Sweden.
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nonlocal Gilbert damping tensor within the torque-torque correlation model2018In: Physical review materials, ISSN 2475-9953, Vol. 2, no 1, article id 013801Article in journal (Refereed)
    Abstract [en]

    An essential property of magnetic devices is the relaxation rate in magnetic switching, which depends strongly on the damping in the magnetization dynamics. It was recently measured that damping depends on the magnetic texture and, consequently, is a nonlocal quantity. The damping enters the Landau-Lifshitz-Gilbert equation as the phenomenological Gilbert damping parameter a, which does not, in a straightforward formulation, account for nonlocality. Efforts were spent recently to obtain Gilbert damping from first principles for magnons of wave vector q. However, to the best of our knowledge, there is no report about real-space nonlocal Gilbert damping aij. Here, a torque-torque correlation model based on a tight-binding approach is applied to the bulk elemental itinerant magnets and it predicts significant off-site Gilbert damping contributions, which could be also negative. Supported by atomistic magnetization dynamics simulations, we reveal the importance of the nonlocal Gilbert damping in atomistic magnetization dynamics. This study gives a deeper understanding of the dynamics of the magnetic moments and dissipation processes in real magnetic materials. Ways of manipulating nonlocal damping are explored, either by temperature, materials doping, or strain.

  • 33.
    Torchio, R.
    et al.
    ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France.;CEA, DAM, DIF, F-91297 Arpajon, France..
    Marini, C.
    ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France.;CELLS, ALBA Synchrotron, E-08290 Cerdanyola Del Valles, Spain..
    Kvashnin, Yaroslav O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France.
    Kantor, I.
    ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France..
    Mathon, O.
    ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France..
    Garbarino, G.
    ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France..
    Meneghini, C.
    Univ ROMA TRE, Dipartimento Sci, Via Vasca Navale 84, Rome, Italy..
    Anzellini, S.
    CEA, DAM, DIF, F-91297 Arpajon, France.;Diamond Light Source Ltd, Diamond House,Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England..
    Occelli, F.
    CEA, DAM, DIF, F-91297 Arpajon, France..
    Bruno, P.
    ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France..
    Dewaele, A.
    CEA, DAM, DIF, F-91297 Arpajon, France..
    Pascarelli, S.
    ESRF European Synchrotron, 71 Ave Martyrs, Grenoble, France..
    Structure and magnetism of cobalt at high pressure and low temperature2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 2, article id 024429Article in journal (Refereed)
    Abstract [en]

    The magnetic and structural properties of cobalt were investigated under high pressure (160 GPa) and low temperature (50 K), by synchrotron K-edge x-ray magnetic circular dichroism and x-ray diffraction. A quasihydrostatic equation of state was measured up to 160 GPa. We found that uniaxial stress plays a role in the hexagonal close packed-face centered cubic (hcp-fcc) structural transition pressure. Also, our data provide the first experimental evidence that changes of the c/a ratio pressure derivative are related to the magnetic behavior. The complete extinction of ferromagnetism is observed above 130 GPa in a mixed hcp-fcc phase with no recovery upon cooling to 50 K, indicating that cobalt at 150 GPa is very likely nonmagnetic, i.e., characterized by zero local spin polarization. Density functional theory calculations point out that the K-edge x-ray magnetic circular dichroism (XMCD) signal is related to the 4p orbital moment rather than to the total spin moment and allow us to get a deeper insight into the K-edge XMCD measurements interpretation. The combination of novel theoretical results and experimental outputs provides a detailed scenario of the structural and magnetic properties of cobalt at these extreme conditions answering some previously unsolved issues.

1 - 33 of 33
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