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  • 1. Arhammar, C.
    et al.
    Silvearv, F.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Norgren, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Pedersen, H.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A theoretical study of possible point defects incorporated into alpha-alumina deposited by chemical vapor deposition2013In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 133, no 2, p. 1433-Article in journal (Refereed)
    Abstract [en]

    The energetics and electronic structure of carbon, chlorine, hydrogen, and sulfur in alpha-Al2O3 was investigated by first principles and thermodynamical calculations. These species are present in the gas phase during the synthesis of alpha-Al2O3 by chemical vapor deposition (CVD) but little is known of their solubility in this compound. The heat of formation from standard reference states of the elements varying the chemical potential of each element was calculated. An attempt to model the actual conditions in the CVD process was made, using the species and solid compounds present in a common CVD process as reference states. Our calculations suggest that sulfur from the catalyzing agent H2S will not solve in alpha-Al2O3 during deposition by CVD. It is found that the neutral chlorine and hydrogen interstitial defects display the lowest heat of formation, 281 and 280 kJ/mol, respectively, at the modeled CVD conditions. This energy is too high in order for neutral defects to form during CVD of alpha-Al2O3 at any significant amounts. The charged defects and their compensation were studied. Carbon substituting oxygen is found to be energetically favored under the modeled CVD conditions, considering carbon dioxide as competing species to solid solubility in alpha-Al2O3 at an energy of -128 kJ/mol. However, care needs to be taken when choosing the possible competing carbon-containing phases. Compensation of carbon substituting for oxygen by oxygen vacancies takes place at 110 kJ/mol from standard reference states, graphite, fcc-Al and O-2. The carbon solubility in Al2O3 is difficult to measure with standard analysis techniques such as X-ray diffraction and energy dispersive X-ray spectroscopy, but several stable compounds in the Al-C-O are available in the literature.

  • 2.
    Arnalds, Unnar B.
    et al.
    Univ Iceland, Inst Sci, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Chico, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stopfel, Henry
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Kapaklis, Vassilios
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Bärenbold, Oliver
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Verschuuren, Marc A.
    Philips Res Labs, Eindhoven, Netherlands..
    Wolff, Ulrike
    IFW Dresden, Inst Metall Mat, D-01171 Dresden, Germany..
    Neu, Volker
    IFW Dresden, Inst Metall Mat, D-01171 Dresden, Germany..
    Bergman, Anders
    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 Physics.
    A new look on the two-dimensional Ising model: thermal artificial spins2016In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 18, article id 023008Article in journal (Refereed)
    Abstract [en]

    We present a direct experimental investigation of the thermal ordering in an artificial analogue of an asymmetric two-dimensional Ising system composed of a rectangular array of nano-fabricated magnetostatically interacting islands. During fabrication and below a critical thickness of the magnetic material the islands are thermally fluctuating and thus the system is able to explore its phase space. Above the critical thickness the islands freeze-in resulting in an arrested thermalized state for the array. Determining the magnetic state we demonstrate a genuine artificial two-dimensional Ising system which can be analyzed in the context of nearest neighbor interactions.

  • 3.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    A Theoretical Study of Magnetism in Nanostructured Materials2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A first-principles linear scaling real-space method for investigating non-collinear magnetic behaviour of nanostructured materials has been developed. With this method, the magnetic structures of small supported transition metal clusters have been examined. The geometric constraints imposed on the clusters by the underlying surface is found to cause non-collinear behaviour for V, Cr, and Mn clusters on Cu(111). Fe clusters supported on Cu and Ni have been studied and both spin and orbital moments are found to be enhanced for the Fe atoms, which is attributed to the recuced symmetry present at the surface. Atoms in Co clusters have been found to order antiferromagnetically, and some times in a non-collinear fasion, when deposited on a W surface. Small clusters of fcc Fe embedded in Cu have been examined and a new type of ordering, not present in larger fcc Fe systems was found.

    Several theoretical studies of Fe and Co based nanostructures consisting of multilayers or embedded clusters have been conducted, with the aim of predicting high moment materials for use in data storage applications. In agreement with previous experiments an enhancement of the magnetic moment is found compared to the magnetic moment of bcc Fe. The enhancement has been shown to be caused by increased spin moments for Fe atoms in close proximity with Co atoms, and this enhancement depends on the number of Co neighbours. As a result of these studies, a possible method of increasing the magnetic moment of cluster based materials has been proposed.

    Fermi surface analysis have been performed both on bulk materials, in order to investigate mechanisms for stabilizing non-collinear magnetic states, and in layered structures where the effect of the Fermi surface on the interlayer exchange coupling has been investigated.

    In addition to the development of a real-space electronic structure method for non-collinear magnetism, a density matrix purification method has been implemented in the framework of linear muffin-tin orbitals.

    List of papers
    1. Linear scaling density matrix approach for the linear muffin-tin orbital method
    Open this publication in new window or tab >>Linear scaling density matrix approach for the linear muffin-tin orbital method
    (English)Manuscript (Other academic)
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94286 (URN)
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2012-03-14Bibliographically approved
    2. Fermi-surface effect on magnetic interlayer coupling
    Open this publication in new window or tab >>Fermi-surface effect on magnetic interlayer coupling
    Show others...
    2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 6, p. 064408-Article in journal (Refereed) Published
    Abstract [en]

    The oscillating magnetic interlayer coupling of Fe over spacer layers consisting of CuxPd1−x alloys is investigated by first principles density functional theory. The amplitude, period, and phase of the coupling, as well as the disorder-induced decay, are analyzed in detail and the consistency to the Ruderman-Kittel-Kasuya-Yoshida theory is discussed. An effect of the Fermi surface nesting strength on the amplitude is established from first principles calculations. An unexpected variation of the phase and disorder-induced decay is obtained and the results are discussed in terms of asymptotics.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94287 (URN)10.1103/PhysRevB.70.064408 (DOI)
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    3. Role of magnetic impurities in Fe/V multilayers
    Open this publication in new window or tab >>Role of magnetic impurities in Fe/V multilayers
    2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 14, p. 144408-Article in journal (Refereed) Published
    Abstract [en]

    We have studied the Fe/V bcc (100) multilayers and the effect of alloying the V spacer layers with various amounts of magnetic impurities (Fe, Co, Ni, and Cr). The study was performed by means of total energy electronic structure calculations. We compare the effect of the different types of impurities and discuss the interlayer exchange coupling in terms of Fermi surface topology and bulk magnetic order. The effect of interface roughness and interface intermixing on the phase diagrams was also studied.

    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-96087 (URN)10.1103/PhysRevB.77.144408 (DOI)000255457300043 ()
    Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2017-12-14Bibliographically approved
    4. Magnetism of Fe/V and Fe/Co multilayers
    Open this publication in new window or tab >>Magnetism of Fe/V and Fe/Co multilayers
    Show others...
    2003 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, no 5, p. S599-S615Article in journal (Refereed) Published
    Abstract [en]

    We discuss in this paper the magnetic and structural parameters of Fe/V and Fe/Co multilayers. The electronic structure, magnetic moments (spin and orbital) and Curie temperatures as well as the magneto-crystalline anisotropy are calculated using first principles theory. Although theory is fairly successful in reproducing the experimental data we argue that the observed difference between theory and experiment most likely is due to lattice imperfections and that the interface between e.g. Fe and V is not perfectly sharp. We also present a model, based on the theory of elasticity, for analysing the structural properties of multilayers.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94289 (URN)10.1088/0953-8984/15/5/313 (DOI)
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    5. Magnetic properties of Fe/Co(001) superlattices from first-principles theory
    Open this publication in new window or tab >>Magnetic properties of Fe/Co(001) superlattices from first-principles theory
    Show others...
    2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 17, p. 174409-Article in journal (Refereed) Published
    Abstract [en]

    The magnetic properties of Fe/Co(001) superlattices have been studied using fully-relativistic first-principles theories. The average magnetic moment shows a behavior similar to bulk Fe-Co alloys, i.e., an enhanced magnetic moment for low Co concentrations, as described by the Slater-Pauling curve. The maximum of the magnetization curve, however, is lowered and shifted towards the Fe-rich compositions. The increased average magnetic moment for the Fe-rich superlattices, compared to bulk Fe, is due to an enhancement of the Fe spin moment close to the Fe-Co interface. The orbital moments were found to be of the same size as in bulk. The effect of interface roughness on the magnetic properties was investigated, and it was found that-despite local fluctuations due to the varying coordination-the average magnetic moment is only slightly affected. From a mapping of first-principles interactions onto the screened generalized perturbation method, we calculate the temperatures for when Fe/Co superlattices break up into an alloy configuration. Furthermore, the tetragonal distortion of the superlattice structure was found to only have a minor effect on the magnetic moments. Also, the calculated easy axis of magnetization is in the film plane for all compositions studied. It lies along the [100] direction for Fe-rich superlattices and along the [110] direction for Co-rich compositions. The transition of the easy axis occurs around a Co concentration of 50%.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94290 (URN)10.1103/PhysRevB.74.174409 (DOI)000242409000080 ()
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    6. Local magnetic effects of interface alloying in Fe/Co multilayers
    Open this publication in new window or tab >>Local magnetic effects of interface alloying in Fe/Co multilayers
    Show others...
    In: Journal of Physics: Condensed MatterArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-94291 (URN)
    Available from: 2006-04-12 Created: 2006-04-12Bibliographically approved
    7. Magnetism of Fe clusters embedded in a Co matrix from first-principles theory
    Open this publication in new window or tab >>Magnetism of Fe clusters embedded in a Co matrix from first-principles theory
    Show others...
    2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 17, p. 174446-Article in journal (Refereed) Published
    Abstract [en]

    We have calculated spin and orbital moments for Fe clusters of sizes up to 700 atoms embedded as impurities in a bcc Co matrix. The calculations have been carried out using relativistic first-principles real-space density functional theory, and we have made a comparison with earlier experimental studies. For Fe atoms close to theFeCo interface, the spin moments are found to increase while atoms far from the interface exhibit bulklike moments. The Co moments remain essentially unchanged and close to the moment of bulk bcc Co. With increasing cluster size, the average moments of the cluster atoms decrease due to the decreased surface to volume ratio. The orbital moments of both Fe and Co are calculated to be small and they stay almost constant regardless of cluster size. Our results for spin moments agree with experimental data but the calculated orbital moments are slightly underestimated. A simplified model indicates that a compound of close-packed Fe clusters surrounded by Co show higher average total moments compared to bulk and multilayer systems with a similar concentration. This increase seems to disappear when cluster-cluster interactions are taken into account. The general trend is that for a given alloy concentration of FexCo1−x, clustering tends to lower the average magnetic moment compared to that of ordered structures and random alloys.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94292 (URN)10.1103/PhysRevB.70.174446 (DOI)
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    8. Magnetic moments of Fe clusters embedded in an Fe-Co alloy
    Open this publication in new window or tab >>Magnetic moments of Fe clusters embedded in an Fe-Co alloy
    2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 10, p. 104422-Article in journal (Refereed) Published
    Abstract [en]

    Motivated by the search for high moment materials, we present first-principles calculations of the magnetic moments for Fe clusters embedded in an Fe-Co alloy as well as in a pure Co matrix. Both spin and orbital contributions have been calculated with the use of a real-space linear muffin-tin orbital method within the atomic sphere approximation. The cluster sizes considered range from 1 to 51 atoms. We find an enhancement of the spin moments of the atoms close to the interface between the cluster and the embedding matrix. The spin moment enhancement is decreasing with increasing Fe content in the surrounding matrix. The slightly lower magnetic moments for the Fe clusters embedded in the Fe rich matrices can nevertheless result in a material with an enhanced saturation magnetization due to the higher moments in the matrix. We argue that the largest average magnetic moments for embedded Fe clusters are obtained for an Fe0.5Co0.5 alloy in the matrix surrounding the clusters.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94293 (URN)10.1103/PhysRevB.74.104422 (DOI)000240872000066 ()
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    9. Conditions for noncollinear instabilities of ferromagnetic materials
    Open this publication in new window or tab >>Conditions for noncollinear instabilities of ferromagnetic materials
    Show others...
    2004 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 10, p. 107205-Article in journal (Refereed) Published
    Abstract [en]

    Two criteria have been identified here which determine whether a magnetic metal orders in a collinear (e.g., ferromagnet) or noncollinear (e.g., spin-spiral) arrangement. These criteria involve the ratio between the strength of the exchange interaction and the width of the electron bands, as well as Fermi-surface nesting between spin-up and spin-down sheets of the Fermi surface. Based on our analysis we predict that even typical ferromagnetic materials (e.g., Fe, Co, and Ni) should be possible to stabilize in a noncollinear magnetic order in, e.g., high pressure experiments.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94356 (URN)10.1103/PhysRevLett.93.107205 (DOI)
    Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2017-12-14Bibliographically approved
    10. Theoretical and experimental study of the magnetic structure of TlCo2Se2
    Open this publication in new window or tab >>Theoretical and experimental study of the magnetic structure of TlCo2Se2
    Show others...
    2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 2, p. 024407-Article in journal (Refereed) Published
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94358 (URN)10.1103/PhysRevB.70.024407 (DOI)
    Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2017-12-14Bibliographically approved
    11. Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0): Experiment and theory
    Open this publication in new window or tab >>Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0): Experiment and theory
    Show others...
    2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 9, p. 094419-Article in journal (Refereed) Published
    Abstract [en]

    The effect of Cu substitution on the structural and magnetic properties of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0) have been investigated by x-ray diffraction, magnetization measurements and neutron powder and single crystal diffraction. The electronic and the magnetic structures of TbNi5 were studied using first principles theory. All samples were found to have the CaCu5-type structure, space group P6/mmm. The lattice parameters increase monotonically with increasing Cu concentration. The Curie temperature T-c has a maximum value of 29 K at x=1.0. The magnetic structure of TbNi5 at 10 K is incommensurate with a helimagnetic component [wave vector q similar to 2 pi/c(0,0,0.02)] perpendicular to a ferromagnetic one. In contrast, the substituted TbNi5-xCux alloy is ferromagnetic. All magnetic moments are observed to be located on the Tb atoms. The magnetocrystalline anisotropy in the ab plane is observed to be strongly increased by the Cu substitution, whereas the magnetization decreases with the Cu concentration. The observed magnetic structure of TbNi5 is consistent with first principles calculations regarding both the magnetic moments and the helimagnetic structure. The microscopical origin of the helimagnet is analyzed and correlated to the Fermi surface topology.

    National Category
    Inorganic Chemistry Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-82093 (URN)10.1103/PhysRevB.74.094419 (DOI)000240871700046 ()
    Available from: 2006-09-18 Created: 2006-09-18 Last updated: 2017-12-14Bibliographically approved
    12. Magnetic structure of a small fcc Fe cluster in Cu
    Open this publication in new window or tab >>Magnetic structure of a small fcc Fe cluster in Cu
    (English)Manuscript (Other academic)
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94297 (URN)
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2012-03-26Bibliographically approved
    13. Magnetic interactions of Mn clusters supported on Cu
    Open this publication in new window or tab >>Magnetic interactions of Mn clusters supported on Cu
    Show others...
    (English)In: Physical Review BArticle in journal (Refereed) Submitted
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94298 (URN)
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2012-03-26Bibliographically approved
    14. Magnetic structure of Fe, Cr, and Mn clusters supported on Cu(111).
    Open this publication in new window or tab >>Magnetic structure of Fe, Cr, and Mn clusters supported on Cu(111).
    Show others...
    (English)Manuscript (Other academic)
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94299 (URN)
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2012-03-26Bibliographically approved
    15. Non-collinear magnetisation of V clusters supported on a Cu (111) surface: Theory
    Open this publication in new window or tab >>Non-collinear magnetisation of V clusters supported on a Cu (111) surface: Theory
    Show others...
    2006 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, no 21, p. 4838-4842Article in journal (Refereed) Published
    Abstract [en]

    Magnetic properties and electronic structure of V clusters supported on a Cu (111) substrate, have been calculated from a first principles method. We observe in general non-collinear magnetic structures that are the result of antiferromagnetic interactions on a frustrated lattice. The values of the magnetic moments range from similar to 0 to 2.7 mu(B)/atom, depending on cluster geometry.

    Keyword
    density functional calculations, vanadium, metal-metal magnetic heterostructures
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94300 (URN)10.1016/j.susc.2006.08.004 (DOI)000242514400007 ()
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    16. Magnetism of Co overlayers and nanostructures on W(001): A first principles study
    Open this publication in new window or tab >>Magnetism of Co overlayers and nanostructures on W(001): A first principles study
    Show others...
    2008 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, no 6, p. 1173-1179Article in journal (Refereed) Published
    Abstract [en]

    The magnetic properties of Co nanostructures and a Co monolayer on W(001) have been studied in the framework of density functional theory. Different geometries such as planar and three-dimensional clusters have been considered, with cluster sizes varying between 2 and 13 atoms. The calculations were performed using the real-space linear muffin-tin orbital method (RS-LMTO-ASA). With respect to the stability of the magnetic state, we predict an antiferromagnetic (AFM) structure for the ground state of the planar Co clusters and a ferromagnetic (FM) state for the three-dimensional clusters. For the three-dimensional clusters, one of the AFM arrangements leads to frustration due to the competing FM and AFM exchange interactions between different atoms in the cluster, and gives rise to a non-collinear state with energy close to that of the FM ground state. The relative role of the Co-Co and Co-W exchange interactions is also investigated.

    Keyword
    density functional calculations, nanoclusters, metal-metal magnetic heterostructures
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94301 (URN)10.1016/j.jmmm.2007.11.011 (DOI)000254416300066 ()
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    17. Spin and orbital moments of Fe clusters supported on Ni(001)
    Open this publication in new window or tab >>Spin and orbital moments of Fe clusters supported on Ni(001)
    Show others...
    2008 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 1, p. 015001-Article in journal (Refereed) Published
    Abstract [en]

    The spin and orbital moments for small Fe clusters deposited on a Ni(001) surface have been calculated by means of an ab initio method. We find enhanced spin and orbital moments compared to what is found in bulk Fe. Our obtained spin moments are in good agreement with previous theoretical studies on similar systems. Comparing our results with a recent x-ray magnetic circular dichroism study (Lau et al 2002 Phys. Rev. Lett. 89 057201), we find that the calculated orbital moments are much lower than those experimentally found. Reasons for this discrepancy are discussed.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94302 (URN)10.1088/0953-8984/20/01/015001 (DOI)000252921800002 ()
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
    18. A first-principles study of the magnetism and electronic structure of Cr clusters supported on a Au(111) surface
    Open this publication in new window or tab >>A first-principles study of the magnetism and electronic structure of Cr clusters supported on a Au(111) surface
    Show others...
    2007 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 15, p. 156226-Article in journal (Refereed) Published
    Abstract [en]

    We have studied clusters of Cr on a Au(111) surface by means of a first-principles method that allows for non-collinear magnetic ordering. We find that the Cr atoms possess a large magnetic moment, of order 4 μB/atom, and have essentially antiferromagnetic interatomic exchange interactions. This leads to collinear magnetic arrangements in linear clusters (dimers and trimers) and non-collinear ordering in clusters where antiferromagnetism becomes frustrated, such as in triangular geometries.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-94303 (URN)10.1088/0953-8984/19/15/156226 (DOI)000245670400032 ()
    Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2017-12-14Bibliographically approved
  • 4.
    Bergman, Anders
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV.
    High moment materials studied by real-space first principles theory2004Licentiate thesis, monograph (Other scientific)
  • 5.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Burkert, Till
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Frota-Pessôa, Sonia
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ruban, Andrei.V.
    Simak, Sergei.I.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Magnetic properties of Fe/Co(001) superlattices from first-principles theory2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 17, p. 174409-Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of Fe/Co(001) superlattices have been studied using fully-relativistic first-principles theories. The average magnetic moment shows a behavior similar to bulk Fe-Co alloys, i.e., an enhanced magnetic moment for low Co concentrations, as described by the Slater-Pauling curve. The maximum of the magnetization curve, however, is lowered and shifted towards the Fe-rich compositions. The increased average magnetic moment for the Fe-rich superlattices, compared to bulk Fe, is due to an enhancement of the Fe spin moment close to the Fe-Co interface. The orbital moments were found to be of the same size as in bulk. The effect of interface roughness on the magnetic properties was investigated, and it was found that-despite local fluctuations due to the varying coordination-the average magnetic moment is only slightly affected. From a mapping of first-principles interactions onto the screened generalized perturbation method, we calculate the temperatures for when Fe/Co superlattices break up into an alloy configuration. Furthermore, the tetragonal distortion of the superlattice structure was found to only have a minor effect on the magnetic moments. Also, the calculated easy axis of magnetization is in the film plane for all compositions studied. It lies along the [100] direction for Fe-rich superlattices and along the [110] direction for Co-rich compositions. The transition of the easy axis occurs around a Co concentration of 50%.

  • 6.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Magnetic moments of Fe clusters embedded in an Fe-Co alloy2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 10, p. 104422-Article in journal (Refereed)
    Abstract [en]

    Motivated by the search for high moment materials, we present first-principles calculations of the magnetic moments for Fe clusters embedded in an Fe-Co alloy as well as in a pure Co matrix. Both spin and orbital contributions have been calculated with the use of a real-space linear muffin-tin orbital method within the atomic sphere approximation. The cluster sizes considered range from 1 to 51 atoms. We find an enhancement of the spin moments of the atoms close to the interface between the cluster and the embedding matrix. The spin moment enhancement is decreasing with increasing Fe content in the surrounding matrix. The slightly lower magnetic moments for the Fe clusters embedded in the Fe rich matrices can nevertheless result in a material with an enhanced saturation magnetization due to the higher moments in the matrix. We argue that the largest average magnetic moments for embedded Fe clusters are obtained for an Fe0.5Co0.5 alloy in the matrix surrounding the clusters.

  • 7.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delin, Anna
    KTH.
    Atomistic spin dynamics of atomic Pt wiresManuscript (preprint) (Other academic)
  • 8.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Holmström, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Niklasson, A.M.N.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Magnetism of Fe clusters embedded in a Co matrix from first-principles theory2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 17, p. 174446-Article in journal (Refereed)
    Abstract [en]

    We have calculated spin and orbital moments for Fe clusters of sizes up to 700 atoms embedded as impurities in a bcc Co matrix. The calculations have been carried out using relativistic first-principles real-space density functional theory, and we have made a comparison with earlier experimental studies. For Fe atoms close to theFeCo interface, the spin moments are found to increase while atoms far from the interface exhibit bulklike moments. The Co moments remain essentially unchanged and close to the moment of bulk bcc Co. With increasing cluster size, the average moments of the cluster atoms decrease due to the decreased surface to volume ratio. The orbital moments of both Fe and Co are calculated to be small and they stay almost constant regardless of cluster size. Our results for spin moments agree with experimental data but the calculated orbital moments are slightly underestimated. A simplified model indicates that a compound of close-packed Fe clusters surrounded by Co show higher average total moments compared to bulk and multilayer systems with a similar concentration. This increase seems to disappear when cluster-cluster interactions are taken into account. The general trend is that for a given alloy concentration of FexCo1−x, clustering tends to lower the average magnetic moment compared to that of ordered structures and random alloys.

  • 9.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Holmström, Erik
    Niklasson, Anders M.N.
    Linear scaling density matrix approach for the linear muffin-tin orbital methodManuscript (Other academic)
  • 10.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Klautau, Angela B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    A first-principles study of the magnetism and electronic structure of Cr clusters supported on a Au(111) surface2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 15, p. 156226-Article in journal (Refereed)
    Abstract [en]

    We have studied clusters of Cr on a Au(111) surface by means of a first-principles method that allows for non-collinear magnetic ordering. We find that the Cr atoms possess a large magnetic moment, of order 4 μB/atom, and have essentially antiferromagnetic interatomic exchange interactions. This leads to collinear magnetic arrangements in linear clusters (dimers and trimers) and non-collinear ordering in clusters where antiferromagnetism becomes frustrated, such as in triangular geometries.

  • 11.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Klautau, Angela B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Non-collinear magnetisation of V clusters supported on a Cu (111) surface: Theory2006In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, no 21, p. 4838-4842Article in journal (Refereed)
    Abstract [en]

    Magnetic properties and electronic structure of V clusters supported on a Cu (111) substrate, have been calculated from a first principles method. We observe in general non-collinear magnetic structures that are the result of antiferromagnetic interactions on a frustrated lattice. The values of the magnetic moments range from similar to 0 to 2.7 mu(B)/atom, depending on cluster geometry.

  • 12.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Klautau, Angela Burlamaqui
    Frota-Pessoa, Sonia
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Magnetic structures of small Fe, Mn, and Cr clusters supported on Cu(111): Noncollinear first-principles calculations2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 22, p. 224425-Article in journal (Refereed)
    Abstract [en]

    The magnetic structures of small clusters of Fe, Mn, and Cr supported on a Cu(111) surface have been studied with noncollinear first-principles theory. Different geometries such as triangles, pyramids, and wires are considered and the cluster sizes have been varied between two and ten atoms. The calculations have been performed using a real-space linear muffin-tin orbital method. The Fe clusters are found to order ferromagnetically regardless of the cluster geometry. For Mn and Cr clusters, antiferromagnetic exchange interactions between nearest neighbors are found to cause collinear antiferromagnetic ordering when the geometry allows it. If the antiferromagnetism is frustrated by the cluster geometry, noncollinear ordering is found. A comparison between the calculated structures and ground states obtained from simplified Heisenberg Hamiltonians show that the exchange interaction varies for different atoms in the clusters as a result of the different local structure.

  • 13.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Klautau, Angela Burlamaqui
    Frota-Pessoa, Sonia
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Magnetism of Co overlayers and nanostructures on W(001): A first principles study2008In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, no 6, p. 1173-1179Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of Co nanostructures and a Co monolayer on W(001) have been studied in the framework of density functional theory. Different geometries such as planar and three-dimensional clusters have been considered, with cluster sizes varying between 2 and 13 atoms. The calculations were performed using the real-space linear muffin-tin orbital method (RS-LMTO-ASA). With respect to the stability of the magnetic state, we predict an antiferromagnetic (AFM) structure for the ground state of the planar Co clusters and a ferromagnetic (FM) state for the three-dimensional clusters. For the three-dimensional clusters, one of the AFM arrangements leads to frustration due to the competing FM and AFM exchange interactions between different atoms in the cluster, and gives rise to a non-collinear state with energy close to that of the FM ground state. The relative role of the Co-Co and Co-W exchange interactions is also investigated.

  • 14. Bergman, Anders
    et al.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Klautau, Angela Burlamaqui
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Magnetic interactions of Mn clusters supported on Cu2006In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 73, no 17, p. 174434-Article in journal (Refereed)
    Abstract [en]

    It is demonstrated that the magnetic interactions can be drastically different for nanosized systems compared to those of bulk or surfaces. Using a real-space formalism we have developed a method to calculate noncollinear magnetization structures and hence exchange interactions. Our results for magnetic Mn clusters supported on a Cu(111) surface show that the magnetic ordering as a rule is noncollinear and cannot always be described by using a simple Heisenberg Hamiltonian. We argue that the use of ab initio calculations allowing for noncollinear coupling between atomic spins constitutes an efficient and reliable way of analyzing nanosized magnets.

  • 15.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Klautau, Angela.B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Magnetic interactions of Mn clusters supported on CuIn: Physical Review BArticle in journal (Refereed)
  • 16.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Klautau, Angela.B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Magnetic structure of Fe, Cr, and Mn clusters supported on Cu(111).Manuscript (Other academic)
  • 17.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Robles, Roberto
    Nordström, Lars
    Magnetic structure of a small fcc Fe cluster in CuManuscript (Other academic)
  • 18.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skubic, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    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.
    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.
    Ultrafast switching in a synthetic antiferromagnetic magnetic random-access memory device2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 22, p. 224429-Article in journal (Refereed)
    Abstract [en]

    The dynamics of a synthetic antiferromagnet (a metallic trilayer) have been explored and are shown to exhibit ultrafast switching on a time scale of tens of ps. This conclusion is based on first-principles, atomistic spin dynamics simulations. The simulations are performed at finite temperature, as well as at T = 0 K (the macrospin limit), and we observe a marked temperature dependence of the switching phenomenon. It is shown that, to reach very high switching speeds, it is important that the two ferromagnetic components of the synthetic antiferromagnet have oppositely directed external fields to one another. Then a complex collaboration between precession switching of an internal exchange field and the damping switching of the external field occurs, which considerably accelerates the magnetization dynamics. We discuss a possible application of this fast switching as a magnetic random access memory device, which has as a key component intrinsic antiferromagnetic couplings and an applied Oersted field.

  • 19.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skubic, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    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.
    Delin, Anna
    KTH.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ultrafast switching in a synthetic antiferromagnetic random-access memory device.Manuscript (preprint) (Other academic)
  • 20.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Taroni, Andrea
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    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 Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Magnon softening in a ferromagnetic monolayer: A first-principles spin dynamics study2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 14, p. 144416-Article in journal (Refereed)
    Abstract [en]

    We study the Fe/W(110) monolayer system through a combination of first-principles calculations and atomistic spin dynamics simulations. We focus on the dispersion of the spin-waves parallel to the [001] direction. Our results compare favorably with the experimental data of Prokop et al. [Phys. Rev. Lett. 102, 177206 (2009)] and correctly capture a drastic softening of the magnon spectrum, with respect to bulk bcc Fe. The suggested shortcoming of the itinerant electron model, in particular that given by density functional theory, is refuted. We also demonstrate that finite-temperature effects are significant, and that atomistic spin dynamics simulations represent a powerful tool with which to include these.

  • 21.
    Bergqvist, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Kudrnovsky, Josef
    Drchal, Vaclav
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Turek, Ilja
    Magnetic properties and disorder effects in diluted magnetic semiconductors2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 19, p. 195210-Article in journal (Refereed)
    Abstract [en]

    We present calculations of the exchange interactions and critical temperatures for several diluted magnetic semiconductor systems. It is shown that the exchange interactions are dominated by short-ranged interactions that have a strong directional dependence. Using a combination of first-principles calculations of the exchange interactions together with Monte Carlo simulations of the classical Heisenberg model, in which the positional disorder and spin fluctuations are properly included, the calculated critical temperatures are in good agreement with experimantal observations. It is shown that agreement between theory and experiment, as regards ordering temperatures, is obtained only when the magnetic atoms are randomly positioned in a simulation cell which proves that disorder effects play a very important role. The effect of strong electron-electron interaction has been studied by means of the LSDA+U scheme. We investigate in detail the nature of the anisotropic exchange interactions by means of a Fermi surface analysis.

  • 22. Bergqvist, Lars
    et al.
    Taroni, Andrea
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Etz, Corina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Olle, Eriksson
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Atomistic spin dynamics of low-dimensional magnets2013In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 87, no 144401Article in journal (Refereed)
    Abstract [en]

    We investigate the magnetic properties of a range of low-dimensional   ferromagnets using a combination of first-principles calculations and   atomistic spin dynamics simulations. This approach allows us to evaluate   the ground state and finite temperature properties of experimentally   well characterized systems such as Co/Cu(111), Co/Cu(001), Fe/Cu(001)   and Fe/W(110), for different thicknesses of the magnetic layer. We   compare our calculated spin wave spectra with experimental data   available in the literature, and find a good quantitative agreement. We   also predict magnon spectra for systems for which no experimental data   exist at the moment, and estimate the role of temperature effects.

  • 23. Bezerra-Neto, Manoel M.
    et al.
    Ribeiro, Marcelo S.
    Sanyal, Biplab
    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.
    Muniz, Roberto B.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Klautau, Angela B.
    Complex magnetic structure of clusters and chains of Ni and Fe on Pt(111)2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 3054-Article in journal (Refereed)
    Abstract [en]

    We present an approach to control the magnetic structure of adatoms adsorbed on a substrate having a high magnetic susceptibility. Using finite Ni-Pt and Fe-Pt nanowires and nanostructures on Pt(111) surfaces, our ab initio results show that it is possible to tune the exchange interaction and magnetic configuration of magnetic adatoms (Fe or Ni) by introducing different numbers of Pt atoms to link them, or by including edge effects. The exchange interaction between Ni (or Fe) adatoms on Pt(111) can be considerably increased by introducing Pt chains to link them. The magnetic ordering can be regulated allowing for ferromagnetic or antiferromagnetic configurations. Noncollinear magnetic alignments can also be stabilized by changing the number of Pt-mediated atoms. An Fe-Pt triangularly-shaped nanostructure adsorbed on Pt(111) shows the most complex magnetic structure of the systems considered here: a spin-spiral type of magnetic order that changes its propagation direction at the triangle vertices.

  • 24.
    Bhattacharjee, Satadeep
    et al.
    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.
    Taroni, Andrea
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    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.
    Theoretical Analysis of Inertia-like Switching in Magnets: Applications to a Synthetic Antiferromagnet2012In: PHYS REV X, ISSN 2160-3308, Vol. 2, no 1, p. 011013-Article in journal (Refereed)
    Abstract [en]

    The magnetization dynamics of a synthetic antiferromagnet subjected to a short-magnetic-field pulse has been studied by using a combination of first principles calculations and atomistic spin-dynamics simulations. We observe switching phenomena on the time scale of tens of picoseconds, and inertia-like behavior in the magnetization dynamics. We explain the latter in terms of a dynamic redistribution of magnetic energy from the applied-field pulse to other possible energy terms, such as the exchange interaction and the magnetic anisotropy, without invoking concepts such as the inertia of an antiferro-magnetic vector. We also demonstrate that such dynamics can also be observed in a ferromagnetic material where the incident-field pulse pumps energy to the magnetic anisotropy.

  • 25.
    Björkman, Torbjörn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Lizárraga, Raquel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Bultmark, Fredrik
    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.
    Wills, John M.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Andersson, Per H.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn52010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 9, p. 094433-Article in journal (Refereed)
    Abstract [en]

    We have investigated the electronic structure and the incommensurate magnetic configuration of the pressure-induced superconductor CeRhIn5. Noncollinear first-principles calculations were performed in the local-density approximation plus U scheme. The observed magnetic configuration is described accurately in our calculations, especially considering the minute energy scale which is relevant (microelectron volt). The band structure and Fermi surfaces were investigated and nesting was found to be responsible for the complex noncollinear magnetic state of CeRhIn5.

  • 26.
    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.

  • 27.
    Cardias, R.
    et al.
    Fed Univ Para, Fac Fis, BR-66059 Belem, PA, Brazil..
    Bezerra-Neto, M. M.
    Fed Univ Para, Fac Fis, BR-66059 Belem, PA, Brazil.;Univ Fed Oeste Para, Inst Engn & Geociencias, Santarem, PA, Brazil..
    Ribeiro, M. S.
    Fed Univ Para, Fac Fis, BR-66059 Belem, PA, Brazil.;Inst Fed Para, Campus Belem, Belem, PA, Brazil..
    Bergman, Anders
    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.
    Eriksson, Olle
    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-66059 Belem, PA, Brazil..
    Magnetic and electronic structure of Mn nanostructures on Ag(111) and Au(111)2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 1, article id 014438Article in journal (Refereed)
    Abstract [en]

    We present results of the electronic and magnetic structure of Mn nanowires adsorbed on Ag(111) and Au(111) surfaces. For finite Mn nanowires on Ag(111) and Au(111) surfaces, our ab initio results show that the large difference between the spin-orbit splitting of these two surfaces leads to completely different magnetic configurations. The magnetic ordering for Mn nanowires adsorbed on Ag(111) is governed by the strong exchange interaction between Mn adatoms. For Mn nano-chains on Au(111), the competition between Heisenberg and Dzyaloshinskii-Moriya interactions leads to a complex magnetic structure of the clusters considered here. Among the more conspicuous results we note a spin-spiral helical type for the nanowire with seven atoms, and a complex magnetic configuration incommensurate with the substrate lattice for a double-sized Mn wire. The effect of the structural relaxation is also investigated, showing sensitivity of the exchange interactions to the bond distance to the substrate. We also demonstrate that small changes in the band filling of these Mn chains results in drastically different changes of the interatomic exchange. Finally, we show that dispersion of the electronic energy spectrum is possible even in nanostructures with bounded spatial extension.

  • 28.
    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.

  • 29.
    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.

  • 30.
    Chico, Jonathan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Etz, Corina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, Lars
    Eriksson, Olle
    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.
    Delin, Anna
    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.
    Thermally driven domain-wall motion in Fe on W(110)2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 1, p. 014434-Article in journal (Refereed)
    Abstract [en]

    It has recently been shown that domain walls (DWs) in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(110) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting this system to thermal gradients we observe a temperature-dependent movement of the domain wall. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. Our material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy, and the exchange interaction and shows that the larger DW velocities are found for materials with broader domain-wall width. The relatively slow DW motion of the Fe/W(110) system is hence primarily caused by its narrow domain-wall width, which results from its large magnetic anisotropy and soft exchange.

  • 31.
    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.

  • 32.
    Chimata, Raghuveer
    et al.
    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
    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.
    Microscopic Model for Ultrafast Remagnetization Dynamics2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 15, p. 157201-Article in journal (Refereed)
    Abstract [en]

    In this Letter, we provide a microscopic model for the ultrafast remagnetization of atomic moments already quenched above the Stoner-Curie temperature by a strong laser fluence. Combining first-principles density functional theory, atomistic spin dynamics utilizing the Landau-Lifshitz-Gilbert equation, and a three-temperature model, we analyze the temporal evolution of atomic moments as well as the macroscopic magnetization of bcc Fe and hcp Co covering a broad time scale, ranging from femtoseconds to picoseconds. Our simulations show a variety of complex temporal behavior of the magnetic properties resulting from an interplay between electron, spin, and lattice subsystems, which causes an intricate time evolution of the atomic moment, where longitudinal and transversal fluctuations result in a macrospin moment that evolves highly nonmonotonically.

  • 33.
    Chimata, Raghuveer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chico, Jonathan
    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.
    Berqvist, Lars
    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.
    Laser heated ferromagnetic simulations2015In: Ultrafast Magnetism I, 2015, p. 76-78Conference paper (Refereed)
    Abstract [en]

    In this work, we show a model of ferromagnetic material heated by a laser pulse. The laser creates a pattern of circles on the ferromagnetic materials with hot regions heated up to 3000K and cold regions at 100K and 400K. In our model the Landau-Lifshitz-Gilbert equation for a macrospin and spin temperature is passed through stochastic field. We show that the difference of magnon dispersion in the cold regions of the material.

  • 34.
    Chimata, Raghuveer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Isaeva, Leyla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kadas, Krisztina
    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.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mentink, Johan H.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Katsnelson, Mikhail I.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Rasing, Theo
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Kirilyuk, Andrei
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Kimel, Alexey
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Eriksson, Olle
    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.
    All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 9, article id 094411Article in journal (Refereed)
    Abstract [en]

    In recent years there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e., first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshinskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbor exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

  • 35.
    Costa, Marcio
    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.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Venezuela, P.
    Instituto de Física, Universidade Federal Fluminense, Rio de Janeiro, Brasilien.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Klintenberg, Mattias
    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.
    Large magnetic anisotropy of Fe2P investigated via ab initio density functional theory calculations2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 8, p. 085125-Article in journal (Refereed)
    Abstract [en]

    We present an investigation of the large magnetic anisotropy of Fe2P, based on ab initio density functional theory calculations, with a full-potential linear muffin-tin orbital basis. We obtain a uniaxial magnetic anisotropy energy (MAE) of 664 mu eV/f.u., which is in decent agreement with experimental observations. Based on a band structure analysis the microscopic origin of the large magnetic anisotropy is explained. We also show that by straining the crystal structure, the MAE can be enhanced further.

  • 36.
    Costa, Marcio
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunstroem, P.
    Di Marco, Igor
    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.
    Klautau, A. B.
    Lichtenstein, A. I.
    Katsnelson, M. I.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Correlated electronic structure of Fe in bulk Cs and on a Cs surface2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 11, p. 115142-Article in journal (Refereed)
    Abstract [en]

    We have investigated the spectral properties of Fe impurities in a Cs host, for both surface and bulk systems, by means of a combination of density functional theory in the local density approximation and dynamical mean-field theory (LDA + DMFT). The effective impurity model arising in LDA + DMFT was solved via two different techniques, i.e., the Hubbard I approximation and the exact diagonalization. It is shown that noticeable differences can be seen in the unoccupied part of the spectrum for different positions of Fe atoms in the host, despite the fact that hybridization between Fe d-states and Cs is low. Our calculations show good agreement with the experimental photoemission spectra reported by Carbone et al. [Carbone, Veronese, Moras, Gardonio, Grazioli, Zhou, Rader, Varykhalov, Krull, Balashov, Mugarza, Gambardella, Lebegue, Eriksson, Katsnelson, and Lichtenstein, Phys. Rev. Lett. 104, 117601 (2010)].

  • 37.
    de Melo Rodrigues, Debora Carvalho
    et al.
    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.
    Bergman, Anders
    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.
    Klautau, Angela Burlamaqui
    Fed Univ Para, Fac Fis, BR-66075110 Belem, Para, Brazil..
    First-principles theory of electronic structure and magnetism of Cr nano-islands on Pd(111)2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 2, article id 025807Article in journal (Refereed)
    Abstract [en]

    We report on the electronic structure, magnetic moments and exchange interactions of one-and two-dimensional Cr clusters on a Pd(1 1 1) substrate, using a real-space method based on density functional theory in the local spin density approximation. We find in general that for the investigated clusters, the magnetic moments are sizeable and almost entirely of spin-character. We demonstrate that the interactions in general are dominated by nearest-neighbor antiferromagnetic Heisenberg form, which implies that Cr on Pd(1 1 1) forms an ideal model system, in which clusters of almost any shape and size can be investigated from a Heisenberg Hamiltonian, using a nearest-neighbor exchange model. We have also found that complex magnetic structures can be realized for linear chains of Cr, due to a competition between exchange interaction and a weaker Dzyaloshinskii-Moriya interaction.

  • 38.
    Durrenfeld, P.
    et al.
    Gothenburg Univ, Dept Phys, S-41296 Gothenburg, Sweden..
    Gerhard, F.
    Univ Wurzburg, Phys Inst EP3, D-97074 Wurzburg, Germany..
    Chico, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dumas, R. K.
    Gothenburg Univ, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Ranjbar, M.
    Gothenburg Univ, Dept Phys, S-41296 Gothenburg, Sweden..
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, L.
    KTH Royal Inst Technol, Mat & Nano Phys, Sch ICT, S-16440 Kista, Sweden.;Swedish e Sci Res Ctr SeRC, S-10044 Stockholm, Sweden..
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Mat & Nano Phys, Sch ICT, S-16440 Kista, Sweden.;Swedish e Sci Res Ctr SeRC, S-10044 Stockholm, Sweden..
    Gould, C.
    Univ Wurzburg, Phys Inst EP3, D-97074 Wurzburg, Germany..
    Molenkamp, L. W.
    Univ Wurzburg, Phys Inst EP3, D-97074 Wurzburg, Germany..
    Akerman, J.
    Gothenburg Univ, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden.;KTH Royal Inst Technol, Mat & Nano Phys, Sch ICT, S-16440 Kista, Sweden..
    Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 21, article id 214424Article in journal (Refereed)
    Abstract [en]

    The half-metallic half-Heusler alloy NiMnSb is a promising candidate for applications in spintronic devices due to its low magnetic damping and its rich anisotropies. Here we use ferromagnetic resonance (FMR) measurements and calculations from first principles to investigate how the composition of the epitaxially grown NiMnSb influences the magnetodynamic properties of saturation magnetization M-S, Gilbert damping alpha, and exchange stiffness A. M-S and A are shown to have a maximum for stoichiometric composition, while the Gilbert damping is minimum. We find excellent quantitative agreement between theory and experiment for M-S and alpha. The calculated A shows the same trend as the experimental data but has a larger magnitude. In addition to the unique in-plane anisotropy of the material, these tunabilities of the magnetodynamic properties can be taken advantage of when employing NiMnSb films in magnonic devices.

  • 39.
    Edström, Alexander
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chico, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jakobsson, Adam
    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.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic structure and magnetic properties of L1(0) binary alloys2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 1, p. 014402-Article in journal (Refereed)
    Abstract [en]

    We present a systematic study of the magnetic properties of L1(0) binary alloys FeNi, CoNi, MnAl, and MnGa via two different density functional theory approaches. Our calculations show large magnetocrystalline anisotropies in the order 1 MJ/m(3) or higher for CoNi, MnAl, and MnGa, while FeNi shows a somewhat lower value in the range 0.48-0.77 MJ/m(3). Saturation magnetization values of 1.3 MA/m, 1.0 MA/m, 0.8 MA/m, and 0.9 MA/m are obtained for FeNi, CoNi, MnAl, and MnGa, respectively. Curie temperatures are evaluated via Monte Carlo simulations and show T-C = 916 K and T-C = 1130 K for FeNi and CoNi, respectively. For Mn-based compounds Mn-rich off-stoichiometric compositions are found to be important for the stability of a ferro- or ferrimagnetic ground state with T-C greater than 600 K. The effect of substitutional disorder is studied and found to decrease both magnetocrystalline anisotropies and Curie temperatures in FeNi and CoNi.

  • 40.
    Eriksson, Olle
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Bergqvist, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Holmström, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Lebacq, Olivier
    Frota-Pessôa, Sonya
    Hjörvarsson, Björgvin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Magnetism of Fe/V and Fe/Co multilayers2003In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, no 5, p. S599-S615Article in journal (Refereed)
    Abstract [en]

    We discuss in this paper the magnetic and structural parameters of Fe/V and Fe/Co multilayers. The electronic structure, magnetic moments (spin and orbital) and Curie temperatures as well as the magneto-crystalline anisotropy are calculated using first principles theory. Although theory is fairly successful in reproducing the experimental data we argue that the observed difference between theory and experiment most likely is due to lattice imperfections and that the interface between e.g. Fe and V is not perfectly sharp. We also present a model, based on the theory of elasticity, for analysing the structural properties of multilayers.

  • 41.
    Etz, Corina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, Lars
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Taroni, Andrea
    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.
    Atomistic spin dynamics and surface magnons2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 24, article id 243202Article, review/survey (Refereed)
    Abstract [en]

    Atomistic spin dynamics simulations have evolved to become a powerful and versatile tool for simulating dynamic properties of magnetic materials. It has a wide range of applications, for instance switching of magnetic states in bulk and nano-magnets, dynamics of topological magnets, such as skyrmions and vortices and domain wall motion. In this review, after a brief summary of the existing investigation tools for the study of magnons, we focus on calculations of spin-wave excitations in low-dimensional magnets and the effect of relativistic and temperature effects in such structures. In general, we find a good agreement between our results and the experimental values. For material specific studies, the atomistic spin dynamics is combined with electronic structure calculations within the density functional theory from which the required parameters are calculated, such as magnetic exchange interactions, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya vectors.

  • 42.
    Etz, Corina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Costa, Marcio
    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.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Accelerating the switching of magnetic nanoclusters by anisotropy-driven magnetization dynamics2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 22, p. 224401-Article in journal (Refereed)
    Abstract [en]

    In this work, the magnetization dynamics of clusters supported on nonmagnetic substrates is shown to exhibit a complex response when subjected to external magnetic fields. The field-driven magnetization reversal of small Co clusters deposited on a Cu(111) surface has been studied by means of first-principles calculations and atomistic spin dynamics simulations. For applied fields ranging from 1 to 10 Tesla, we observe a coherent magnetization reversal with switching times in the range of several tenths of picoseconds to several nanoseconds, depending on the field strength. We find a nonmonotonous dependence of the switching times with respect to the strength of the applied field, which we prove has its origin in the complex magnetic anisotropy landscape of these low-dimensional systems. This effect is shown to be stable for temperatures around 10 K, and is possible to realize over a range of exchange interactions and anisotropy landscapes. Possible experimental routes to achieve this unique switching behavior are discussed.

  • 43. Ganguly, Shreemoyee
    et al.
    Costa, Marcio
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Klautau, Angela B.
    Bergman, Anders
    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.
    Mookerjee, Abhijit
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Augmented space recursion formulation of the study of disordered alloys with noncollinear magnetism and spin-orbit coupling: Application to MnPt and Mn3Rh2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 9, p. 094407-Article in journal (Refereed)
    Abstract [en]

    We have developed a formalism by combining the tight binding linearized muffin-tin orbital and the recursion methods with the augmented space formalism (TB-LMTO-ASR) to study noncollinear magnetism in disordered alloys. We apply the TB-LMTO-ASR to study disordered MnPt and Mn3Rh alloys. The electronic structures of these alloys in different magnetic structures have been calculated and compared to the previous theoretical results.

  • 44. Hellsvik, J.
    et al.
    Balestieri, M.
    Usui, T.
    Stroppa, A.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergqvist, L.
    Prabhakaran, D.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Picozzi, S.
    Kimura, T.
    Lorenzana, J.
    Tuning order-by-disorder multiferroicity in CuO by doping2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 1, p. 014437-Article in journal (Refereed)
    Abstract [en]

    The high Curie temperature multiferroic compound CuO has a quasidegenerate magnetic ground state that makes it prone to manipulation by the so-called "order-by-disorder" mechanism. First principle computations supplemented with Monte Carlo simulations and experiments show that isovalent doping allows us to stabilize the multiferroic phase in nonferroelectric regions of the pristine material phase diagram with experiments reaching a 250% widening of the ferroelectric temperature window with 5% of Zn doping. Our results allow us to validate the importance of a quasidegenerate ground state on promoting multiferroicity on CuO at high temperatures and open a path to the material engineering of multiferroic materials. In addition we present a complete explanation of the CuO phase diagram and a computation on the incommensurability in excellent agreement with experiment without free parameters.

  • 45.
    Hellsvik, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mentink, Johan
    Radboud University Nijmegen.
    Bergqvist, Lars
    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.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rasing, Theo
    Radboud University Nijmegen.
    Katsnelson, Mikhail
    Radboud University Nijmegen.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Atomistic spin dynamics simulations of ferrimagnetic relaxationManuscript (preprint) (Other academic)
  • 46.
    Hellsvik, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Taroni, Andrea
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kudrnovsky, Josef
    Institute of Physics, ASCR.
    Excitation spectra of the frustrated ZnMnSe and CdMnTe spin glass alloysManuscript (preprint) (Other academic)
  • 47.
    Holmström, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Abrikosov, Igor A.
    Dugdale, S.B.
    Györffy, B.L.
    Fermi-surface effect on magnetic interlayer coupling2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 6, p. 064408-Article in journal (Refereed)
    Abstract [en]

    The oscillating magnetic interlayer coupling of Fe over spacer layers consisting of CuxPd1−x alloys is investigated by first principles density functional theory. The amplitude, period, and phase of the coupling, as well as the disorder-induced decay, are analyzed in detail and the consistency to the Ruderman-Kittel-Kasuya-Yoshida theory is discussed. An effect of the Fermi surface nesting strength on the amplitude is established from first principles calculations. An unexpected variation of the phase and disorder-induced decay is obtained and the results are discussed in terms of asymptotics.

  • 48. Igarashi, R. N.
    et al.
    Bezerra Neto, M. M.
    Eleno, L. T. F.
    Bergman, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Klautau, A. B.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Petrilli, H. M.
    Magnetic properties of FexCo1-x nanochains on Pt(111) surfaces2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 20, p. 206003-Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of FexCo1-x nanochains on Pt(1 1 1) were studied using the first-principles real-space linear muffin-tin orbital-atomic sphere approximation (RS-LMTO-ASA) method within the density functional theory. The relative amounts of Fe and Co atoms in a chosen nanochain were varied and several possible arrangements of the atomic species were taken into account. The results of the exchange interaction demonstrates ferromagnetic coupling for the nanowires. Our calculations of Fe and Co average magnetic moments reveal a large enhancement of both spin and orbital moments compared to Fe-Co films deposited on a Pt(1 1 1) surface. The trend for the orbital moments with respect to stoichiometry differs from all previous higher-dimensional Fe-Co alloys on Pt(1 1 1) studies.

  • 49.
    Kadas, Krisztina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Teles da Costa, Marcio
    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.
    Andersson, Yvonne
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Bergman, Anders
    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.
    On the icosahedral metal-phosphorus coordination in melliniite: a gift from the sky for materials chemistry2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 29, p. 14741-14745Article in journal (Refereed)
    Abstract [en]

    Recently a new mineral, melliniite, was reported from a meteorite sample. This mineral has an ideal chemical composition of (Ni,Fe)(4)P and a crystal structure where the phosphorus atoms are coordinated by twelve nearest neighboring metal atoms. No other phosphide has been reported to have such high metal coordination. Therefore melliniite provides new and important information about the chemical interaction in transition metal chalcogenides and possibly pnictides. We demonstrate here, using first principles theory, that the stability and icosahedral metal-phosphorous coordination of melliniite are due to a balance between covalent Fe-P binding, configurational entropy and a weaker nickel-phosphorus binding, that has only a weak directional dependence.

  • 50.
    Kamali, Saeed
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
    Bergman, Anders
    Andersson, Gabriella
    Stanciu, Victor
    Häggström, Lennart
    Local Magnetic Effects of Surface Alloying in Fe/Co SuperlatticesManuscript (Other (popular science, discussion, etc.))
12 1 - 50 of 68
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