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  • 1. Andersson, Gabriella
    et al.
    Burkert, Till
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Warnicke, Peter
    Björck, Matts
    Sanyal, Biplab
    Chacon, Cyril
    Zlotea, Claudia
    Nordström, Lars
    Nordblad, Per
    Eriksson, Olle
    A new alloy for information storageIn: Nature MaterialsArticle in journal (Refereed)
  • 2.
    Andersson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
    Burkert, Till
    Warnicke, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Björck, Matts
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Chacon, Cyril
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Zlotea, Claudia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Perpendicular magnetocrystalline anisotropy in tetragonally distorted Fe-Co alloys2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, no 3, article id 037205Article in journal (Refereed)
    Abstract [en]

    We report on the experimental realization of tetragonal Fe-Co alloys as a constituent of Fe(0.36)Co(0.64)/Pt superlattices with huge perpendicular magnetocrystalline anisotropy energy, reaching 210 mu eV/atom, and a saturation magnetization of 2.5 mu(B)/atom at 40 K, in qualitative agreement with theoretical predictions. At room temperature the corresponding values 150 mu eV/atom and 2.2 mu(B)/atom are achieved. This suggests that Fe-Co alloys with carefully chosen combinations of composition and distortion are good candidates for high-density perpendicular storage materials.

  • 3.
    Andersson, P. H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Eriksson, Olle
    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.
    The effect of hydrogenation on the crystal structure and magnetic state in Pd3Mn2001In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 226-230, no Part 1, p. 1040-1041Article in journal (Refereed)
    Abstract [en]

    The effect of hydrogenation on the crystalstructure and magneticstate of Pd3Mn has been calculated using a full-potential linear augmented plane wave method in the local spin density approximation.When hydrogenated the system is observed to transform from the tetragonal Al3Zr structure to the cubic Cu3Au structure. When hydrogen is removed the system remains in a meta-stable cubic phase for an extended period of time. The structural transformations are associated with a change in the magneticstate. Our theoretical results of magnetic as well as crystalstructure stability are in agreement with experiments, especially the destabilization of the tetragonal structure for increased hydrogen concentration and complex magneticstructure of the cubic phases. The latter is analyzed in terms of Fermi surface nesting.

  • 4.
    Andersson, P. H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Possible magnetic states of vanadium films: theoryManuscript (Other academic)
  • 5.
    Andersson, P. H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Mohn, P.
    Eriksson, Olle
    Theoretical investigation of a pressure induced phase transition in EuCo2P2Manuscript (Other academic)
  • 6.
    Andersson, Per H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Fast, Lars
    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.
    Johansson, Börje
    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.
    Theoretical study of structural and electronic properties of VHx1998In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 58, no 9, p. 5230-5235Article in journal (Refereed)
    Abstract [en]

    We have calculated the change in the electronic structure and the distortion of the lattice in vanadium upon hydrogenation from first principles using the full-potential linear muffin-tin-orbital method and the linear augmented plane-wave method in the local-density approximation. The calculated hydrogen induced volume expansions agree with experiment and the change in the c/a ratio is also in good agreement with observations where such are available for single phase VHx. Among several changes in the electronic structure, we note a hybridization of the d band of vanadium with the hydrogen 1s band. We also observe an antiferromagnetically ordered moment at V/Vexp=1.08. The possibility of producing magnetic V by means of hydrogenation in combination with epitaxial growth is suggested.

  • 7.
    Andersson, Per H.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Effect of hydrogenation on the magnetic state in cubic Pd3Mn1999In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 60, no 9, p. 6765-6769Article in journal (Refereed)
    Abstract [en]

    The effect of hydrogenation on the magnetic and electronic state of cubic Pd3Mn has been calculated using a full-potential linear augmented plane-wave method in the local spin-density approximation. A complex magnetic structure is found in very good agreement with experiment. For the nonhydrogenated system we observe a noncommensurate spin spiral although we cannot identify the ground state of the spin structure as the total energy of the trigonal spin structure is almost degenerate with the total energy of the tetragonal spin structure. When hydrogenated the direction of the spiral is aligned along the (001) axis. The spin structures agree with experiment and are connected to features on the calculated Fermi surfaces.

  • 8.
    Arvanitis, Dimitri
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Arvanitis, Dimitri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Konishi, Takehisa
    Holub Krappe, Elisabeth
    Hunter Dunn, Jonathan
    Influence of ligand states on the relationship between orbital moment and magnetocrystalline anisotropy2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 17, p. 177207-Article in journal (Refereed)
    Abstract [en]

    The spin and orbital moments of Au/Co/Au trilayers grown on a W(110) single crystal substrate have been investigated by means of x-ray magnetic circular dichroism. Our findings suggest that the orbital moment of Co does not obtain a maximum value along the easy axis, in contrast with previous experience. This is attributed to the large spin-orbit interaction within the Au caps. Both second order perturbation theory and first principles calculations show how the magnetocrystalline anisotropy (MCA) is dramatically influenced by this effect, and how this leads to the fact that the orbital moment anisotropy is not proportional to the MCA.

  • 9.
    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%.

  • 10.
    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.

  • 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.
    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.

  • 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, 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.

  • 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.
    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.

  • 14.
    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.

  • 15. 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.

  • 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 interactions of Mn clusters supported on CuIn: Physical Review BArticle in journal (Refereed)
  • 17.
    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)
  • 18.
    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)
  • 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
    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.

  • 20.
    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)
  • 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.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Korzhavyi, Pavel
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Mirbt, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Abrikosov, Igor
    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, Condensed Matter Theory.
    Smirnova, E.
    Mohn, Peter
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Magnetic and electronic structure of (Ga1-xMnx)As2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 20, p. 205201-Article in journal (Refereed)
  • 23.
    Bhandary, Sumanta
    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.
    Szunyogh, Laszlo
    Sanyal, Biplab
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Route towards finding large magnetic anisotropy in nanocomposites: Application to a W(1-x)Re(x)/Fe multilayer2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 9, p. 092401-Article in journal (Refereed)
    Abstract [en]

    We suggest here a nanolaminate, 5[Fe]/2[W(x)Re(1-x)] (x = 0.6-0.8), with enhanced magnetic hardness in combination with a large saturation moment. The calculated magnetic anisotropy of this material reaches values of 5.3-7.0 MJ/m(3), depending on alloying conditions. We also propose a recipe in how to identify other novel magnetic materials, such as nanolaminates and multilayers, with large magnetic anisotropy in combination with a high saturation moment.

  • 24.
    Bhattacharjee, Satadeep
    et al.
    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.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Atomistic Spin Dynamic Method with both Damping and Moment of Inertia Effects Included from First Principles2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 5, p. 057204-Article in journal (Refereed)
    Abstract [en]

    We consider spin dynamics for implementation in an atomistic framework and we address the feasibility of capturing processes in the femtosecond regime by inclusion of moment of inertia. In the spirit of an s-d-like interaction between the magnetization and electron spin, we derive a generalized equation of motion for the magnetization dynamics in the semiclassical limit, which is nonlocal in both space and time. Using this result we retain a generalized Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and demonstrate how the exchange interaction, damping, and moment of inertia, all can be calculated from first principles.

  • 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.
    Bultmark, F.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Dewhurst, K.
    Singh, D. J.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Tests of the efficiency of an augmented distorted planewave basis in electronic structure calculations2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 23, p. 235241-Article in journal (Refereed)
    Abstract [en]

    An augmented distorted planewave plus local orbital basis set has been developed and implemented in a simple fashion in order to test its efficiency for electronic structure calculations. It is based on the idea of using distorted planewaves (Gygi 1993 Phys. Rev. B 48 11692) as basis functions in the interstitial region instead of ordinary planewaves, as in the usual linearized augmented planewave and augmented planewave plus local orbitals methods. This is shown to lead to a significantly more rapid convergence for open structures as well as a modestly improved convergence for close packed structures.

  • 27.
    Bultmark, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Cricchio, Francesco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Multipole decomposition of LDA+U energy and its application to actinides compounds2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 3, p. 035121-Article in journal (Refereed)
    Abstract [en]

    A general reformulation of the exchange energy of 5f shell is applied   in the analysis of the magnetic structure of various actinides compounds in the framework of LDA + U method. The calculations are   performed in a convenient scheme with essentially only one free   parameter, the screening length. The results are analyzed in terms of  different polarization channels due to different multipoles. Generally   it is found that the spin-orbital polarization is dominating. This can   be viewed as a strong enhancement of the spin-orbit coupling in these   systems. This leads to a drastic decrease in spin polarization in   accordance with experiments. The calculations are able to correctly   differentiate magnetic and nonmagnetic Pu system. Finally, in all   magnetic systems an unusual multipolar order is observed, whose   polarization energy is often larger in magnitude than the one of spin polarization.

  • 28.
    Burkert, Till
    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.
    James, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Simak, Sergei I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    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, Condensed Matter Theory.
    Calculation of uniaxial magnetic anisotropy energy of tetragonal and trigonal Fe, Co, and Ni2004In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 69, no 10, p. 104426-Article in journal (Refereed)
  • 29.
    Burkert, Till
    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.
    Simak, Sergei I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ruban, Andrei V.
    Sanyal, Biplab
    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.
    Wills, John M.
    Magnetic anisotropy of L10 FePt and Fe1-xMnxPt2005In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 71, no 13, p. 134411-Article in journal (Refereed)
    Abstract [en]

    The uniaxial magnetic anisotropy energy (MAE) of L10 FePt and Fe1−xMnxPt, x=0−0.25, was studied from first principles using two fully relativistic computational methods, the full-potential linear muffin-tin orbitals method and the exact muffin-tin orbitals method. It was found that the large MAE of 2.8 meV/f.u. is caused by a delicate interaction between the Fe and Pt atoms, where the large spin-orbit coupling of the Pt site and the hybridization between Fe 3d and Pt 5d states is crucial. The effect of random order on the MAE was modeled by mutual alloying of the sublattices within the coherent potential approximation (CPA), and a strong dependence of the MAE on the degree of chemical long-range order was found. The alloying of FePt with Mn was investigated with the virtual crystal approximation and the CPA as well as supercell calculations. The MAE increases up to 33% within the concentration range studied here, an effect that is attributed to band filling. Furthermore, the dependence of the MAE on the structural properties was studied.

  • 30.
    Burkert, Till
    et al.
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Heinonen, Olle
    Giant Magnetic Anisotropy in Tetragonal FeCo Alloys2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 2, p. 027203-Article in journal (Refereed)
    Abstract [en]

    The magnetic anisotropy energy (MAE) of hcp Gd was calculated from first principles using the full-potential linear muffin-tin orbital method. It was found that the principal contributions to the MAE are the dipole-dipole interaction between the localized 4f spins and the spin-orbit interaction of the valence band states. The dipole contribution has the form 1/2K(1)(d)(1-cos 2 theta), where theta is the angle between the magnetization direction and the c axis. The contribution of the spin-orbit interaction is shown to arise from the polarization of the conduction band that becomes exchange split due to exchange interaction with the localized 4f electrons. We argue that this leads to significant contributions from higher order anisotropy constants. An imposed reduced 4f moment leads to a repopulation of the electronic states at the Fermi level and a reduced exchange splitting of the valence states, which we demonstrate leads to a modification of the MAE. This modification is in qualitative agreement with the observed temperature dependence of the MAE. In addition, the dependence of the MAE on the c/a ratio has been studied.

  • 31.
    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.

  • 32.
    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.

  • 33.
    Colarieti-Tosti, M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Nordström, Lars
    Brooks, Michael S. S.
    Theory of the Temperature Dependence of the Easy Axis of Magnetization in Gd MetalIn: Physical Review BArticle in journal (Refereed)
  • 34.
    Colarieti-Tosti, M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Nordström, Lars
    Brooks, Michael S. S.
    Wills, J. M.
    Crystal Field Levels and Magnetic Susceptibility in PuO22002In: Physical Review B, Vol. 65, p. 195102-195108Article in journal (Refereed)
  • 35.
    Colarieti-Tosti, M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Eriksson, Olle
    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.
    Brooks, Michael S. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Wills, J. M.
    Crystal field levels in lanthanide systems2001In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 226-230, no Part 1, p. 1027-1028Article in journal (Refereed)
    Abstract [en]

    Crystalfieldlevels in lanthanide compounds have been calculated by first-principles theory, combining the strength of the standard model for rare earths in treating the localized 4f electrons and the power of Density Functional Theory in describing the, weakly correlated, delocalized, electrons. The stability of our calculations has been checked against changes of the constraints in the Full Potential-LMTO implementation. The assumption of weak 4f–4f inter-atomic interactions has also been checked by means of supercell calculations. Suggestions for the treatment of magnetic systems on a similar basis are given.

  • 36.
    Colarieti-Tosti, M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Nordström, Lars
    Wills, J.M
    Brooks, Michael S.S
    Crystal field levels and magnetic susceptibility of PuO$_2$: theory2002In: Phys. Rev. B, Vol. 65, p. 195102-Article in journal (Other academic)
  • 37.
    Colarieti-Tosti, M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Simak, S. I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Åberg, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Edvardsson, S.
    Brooks, Michael S. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Origin of Magnetic Anisotropy of Gd Metal2003In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 91, no 15, p. 157201-157204Article in journal (Refereed)
    Abstract [en]

    Using first-principles theory, we have calculated the energy of Gd as a function of spin direction, θ, between the c and a axes and found good agreement with experiment for both the total magnetic anisotropy energy and its angular dependence. The calculated low temperature direction of the magnetic moment lies at an angle of 20° to the c axis. The calculated magnetic anisotropy energy of Gd metal is due to a unique mechanism involving a contribution of 7.5  μeV from the classical dipole-dipole interaction between spins plus a contribution of 16  μeV due to the spin-orbit interaction of the conduction electrons. The 4f spin polarizes the conduction electrons via exchange interaction, which transfers the magnetic anisotropy of the conduction electrons to the 4f spin.

  • 38.
    Colarieti-Tosti, Massimiliano
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Burkert, Till
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Brooks, Michael S. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Theory of the temperature dependence of the easy axis of magnetization in hcp Gd2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 9, p. 094423-Article in journal (Refereed)
    Abstract [en]

    The magnetic anisotropy energy (MAE) of hcp Gd was calculated from first principles using the full-potential linear muffin-tin orbital method. It was found that the principal contributions to the MAE are the dipole-dipole interaction between the localized 4f spins and the spin-orbit interaction of the valence band states. The dipole contribution has the form 1/2K(1)(d)(1-cos 2 theta), where theta is the angle between the magnetization direction and the c axis. The contribution of the spin-orbit interaction is shown to arise from the polarization of the conduction band that becomes exchange split due to exchange interaction with the localized 4f electrons. We argue that this leads to significant contributions from higher order anisotropy constants. An imposed reduced 4f moment leads to a repopulation of the electronic states at the Fermi level and a reduced exchange splitting of the valence states, which we demonstrate leads to a modification of the MAE. This modification is in qualitative agreement with the observed temperature dependence of the MAE. In addition, the dependence of the MAE on the c/a ratio has been studied.

  • 39.
    Colarieti-Tosti, Massimiliano
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Simak, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV. 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. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV. 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. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Edwardsson, Sverker
    Brooks, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    On the magnetic anisotropy of Gd metal2003In: Physical Review Letters, Vol. 91, p. 157201-Article in journal (Refereed)
  • 40.
    Cricchio, Francesco
    et al.
    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.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Itinerant Magnetic Multipole Moments of Rank Five as the Hidden Order in URu2Si22009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 10, p. 107202-Article in journal (Refereed)
    Abstract [en]

    A broken symmetry ground state without any magnetic moments has been   calculated by means of the local-density approximation to density   functional theory plus a local exchange term, the so-called LDA+U   approach, for URu2Si2. The solution is analyzed in terms of a multipole   tensor expansion of the itinerant density matrix and is found to be a   nontrivial magnetic multipole. Analysis and further calculations show   that this type of multipole enters naturally in time reversal breaking   in the presence of large effective spin-orbit coupling and coexists   with magnetic moments for most magnetic actinides.

  • 41.
    Cricchio, Francesco
    et al.
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Exchange energy dominated by large orbital spin-currents in δ-Pu2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 10, p. 100404-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the anomalous delta phase of Pu is analyzed by a general and exact reformulation of the exchange energy of the f shell. It is found that the dominating contribution to the exchange energy is a polarization of orbital spin-currents that preserves the time-reversal symmetry; hence a nonmagnetic solution in accordance with experiments. The analysis brings a unifying picture of the role of exchange in the 5f shell with its relatively strong spin-orbit coupling. The results are in good accordance with recent measurements of the branching ratio for the d to f transition in the actinides.

  • 42.
    Cricchio, Francesco
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Low spin moment due to hidden multipole order from spin-orbital ordering in LaFeAsO2010In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 14, p. 140403-Article in journal (Refereed)
    Abstract [en]

    An antiferromagnetic (AF) low-moment solution, 0.35 μB / Fe, is found in the case of LaOFeAs for an intermediately strong Coulomb interaction U of 2.75 eV. This solution is stabilized over a large moment solution due to the gain in exchange energy in the formation of large multipoles of the spin magnetization density. The multipoles are of rank four and can be understood as a type of spin-orbital ordering. Parallels can be drawn to the stabilization of the AF order in, e.g., CaCuO2.

  • 43.
    Cricchio, Francesco
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Multipolar and orbital ordering in ferro-pnictidesManuscript (preprint) (Other academic)
    Abstract [en]

    The stability of different solutions corresponding to various arrangement of magnetic rank-4 multipoles are evaluated for the ferro-pnictides LaOFeAs, BaFe2As2 and CaFe2As2 compounds. For LaOFeAs, the ground-state solution is identified with a combination of large w4120 and w4120 multipole tensors of the magnetization density which integrates to the correct value of experimental moment. The same procedure is applied to BaFe2As2 and CaFe2 As2 where the lowest energy solution corresponds again to a combination of w4120 and w4120 multipoles, but with a magnetic moment lower than the experimental value. However, for these compounds, our calculated moment constitutes a significant improvement over previous ab-initio calculations that largely overestimate the Fe moment. Moreover for BaFe2As2 and CaFe2As2 , in the total energy curves as function of constrained spin moment, we identify a local minima close to the experimental moment.

  • 44.
    Cricchio, Francesco
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Multipolar magnetic ordering in actinide dioxides from first-principles calculationsManuscript (preprint) (Other academic)
    Abstract [en]

    The LDA+U method and its multipole decomposition are applied to investigate the ground state of the actinide insulators dioxides UO2 , NpO2 and PuO2 . In case of UO2 , an antifer- romagnetic 3-k type ordering of U moments is identified as one of the lowest energy solutions, in agreement with experiments and recent calculations. For NpO2 , a magnetic multipolar 3-k ordering of triakontadipoles, with a zero net magnetic moment on Np atoms, is found to be one of the most stable solutions. This is in agreement with recent investigations that predict the triakontadipoles to be the hidden order parameter in NpO2 . Also in case of the non-magnetic insulator PuO2 , the ground-state is predicted to be described by a multipolar 1-k ordering of triakontadipoles associated with a magnetization density that integrates to zero on Pu sites.

  • 45.
    Cricchio, Francesco
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Polarization of an open shell in the presence of spin-orbit coupling2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 94, no 5, p. 57009-Article in journal (Refereed)
    Abstract [en]

    There exist many f transition metal-based materials, with large orbital degeneracy and relatively strong spin-orbit coupling, that exhibits some multipolar order. We perform first-principles calculations on these systems within DFT method plus on-site Coulomb correction and we discuss the results in terms of polarization of the density occupation matrix. The fact that higher multipole polarizations play a larger role than the spin polarization indicates a breakdown of Hund's rules and we suggest a new complementary set of rules -Katt's rules, valid in case of large spin-orbit coupling interaction.

  • 46.
    Cricchio, Francesco
    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.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    The role of triakontadipoles in uranium-based magnetic superconductor materialsManuscript (preprint) (Other academic)
    Abstract [en]

    We investigate the ground state of the heavy-fermion actinide compounds UPd2Al3 , UNi2Al3 and UPt3 by means of electronic structure calculations including on-site correlation. The results are analyzed through multipole decomposition. In case of UPd2Al3 and UNi2Al3 we stabilize a solution with an antiferromagnetic arrangement of triakontadipoles with ordering vectors, respectively, q = (0, 0, 1/2 ) and q = ( 1/2 , 0, 1/2 ), whose total magnetic moment agrees with the experimental value. In case of UPt3 we identify a solution with a triakontadipole order whose symmetry is not compatible with the presence of a magnetic moment, in accordance with experiments that detect a very small value of the moment. The Fermi surfaces of the multipole dominated solutions have many common features with those obtained by conventional density functional methods. Finally, for URu2Si2 we are able to stabilize a new solution characterized by a q = (0, 0, 1/2 ) ordering of triakontadipoles and a symmetry that forbids a magnetic moment on uranium site. The Fermi surface of this solution is surprisingly similar to the one of the magnetic AF 1-q case in agreement with recent measurements.

  • 47.
    Enkovaara, J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ayuela, A.
    Nordström, Lars
    Nieminen, R.M.
    Magnetic anisotropy in Ni2MnG2002In: Phys. Rev. B, Vol. 65, p. 134422-Article in journal (Other academic)
  • 48.
    Enkovaara, J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ayuela, A.
    Nordström, Lars
    Nieminen, R.M
    Structural, thermal, and magnetic properties of Ni2MnGa2002In: J. Appl. Phys., Vol. 91, p. 7798-Article in journal (Other academic)
  • 49. Enkovaara, Jussi
    et al.
    Ayuela, Andres
    Jaklanen, J.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Nieminen, Risto
    First-principles calculations of spin spirals in Ni2MnGa and Ni2MnAl2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 5, p. 054417-Article in journal (Refereed)
    Abstract [en]

    We report here noncollinear magnetic configurations in the Heusler alloys Ni2MnGa and Ni2MnAl which are interesting in the context of the magnetic shape memory effect. The total energies for different spin spirals are calculated and the ground-state magnetic structures are identified. The calculated dispersion curves are used to estimate the Curie temperature which is found to be in good agreement with experiments. In addition, the variation of the magnetic moment as a function of the spiral structure is studied. Most of the variation is associated with Ni, and symmetry constraints relevant for the magnetization are identified. Based on the calculated results, the effect of the constituent atoms in determining the Curie temperature is discussed.

  • 50.
    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.

123 1 - 50 of 131
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