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  • 1.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lebègue, Sébastien
    Laboratoire de Cristallographie, Résonance Magnétique et Modélisations, Institut Jean Barriol, Nancy Université, Vandoeuvre-lès-Nancy, France.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adsorption of Cu, Ag, and Au atoms on graphene including van der Waals interactions2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 39, article id 395001Article in journal (Refereed)
    Abstract [en]

    We performed a systematic density functional (DF) study of the adsorption of copper, silver, and gold adatoms on pristine graphene, especially accounting for van der Waals (vdW) interactions by the vdW-DF and PBE + D2 methods. In particular, we analyze the preferred adsorption site (among top, bridge, and hollow positions) together with the corresponding distortion of the graphene sheet and identify diffusion paths. Both vdW schemes show that the coinage metal atoms do bind to the graphene sheet and that in some cases the buckling of the graphene layer can be significant. Only the results for silver are qualitatively at variance with those obtained with the generalized gradient approximation, which gives no binding in this case. However in all three cases, we observe some quantitative differences between the vdW-DF and PBE + D2 methods. For instance the adsorption energies calculated with the PBE + D2 method are systematically higher than the ones obtained with vdW-DF. Moreover, the equilibrium distances computed with PBE + D2 are shorter than those calculated with the vdW-DF method.

  • 2.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Small gold clusters on graphene, their mobility and clustering: a DFT study2011In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 23, no 20, p. 205301-Article in journal (Refereed)
    Abstract [en]

    Motivated by the experimentally observed high mobility of gold atoms on graphene and their tendency to form nanometer-sized clusters, we present a density functional theory study of the ground state structures of small gold clusters on graphene, their mobility and clustering. Our detailed analysis of the electronic structures identifies the opportunity to form strong gold-gold bonds and the graphene-mediated interaction of the pre-adsorbed fragments as the driving forces behind gold's tendency to aggregate on graphene. While clusters containing up to three gold atoms have one unambiguous ground state structure, both gas phase isomers of a cluster with four gold atoms can be found on graphene. In the gas phase the diamond-shaped Au-4(D) cluster is the ground state structure, whereas the Y-shaped Au-4(Y) becomes the actual ground state when adsorbed on graphene. As we show, both clusters can be produced on graphene by two distinct clustering processes. We also studied in detail the stepwise formation of a gold dimer out of two pre-adsorbed adatoms, as well as the formation of Au-3. All reactions are exothermic and no further activation barriers, apart from the diffusion barriers, were found. The diffusion barriers of all studied clusters range from 4 to 36 meV only, and are substantially exceeded by the adsorption energies of -0.1 to -0.59 eV. This explains the high mobility of Au1-4 on graphene along the C-C bonds.

  • 3. 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)
  • 4.
    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.

  • 5.
    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.

  • 6.
    Andersson, P. H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Klintenberg, Mattias
    Henningsson, A.
    Siegbahn, H.
    Eriksson, Olle
    Charge transfer effets in x-ray absorption spectroscopy of transition metal oxidesIn: Phys. Rev. Lett.Article in journal (Refereed)
  • 7.
    Andersson, P H
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Klintenberg, Mattias
    Henningsson, A
    Siegbahn, H
    Eriksson, Olle
    Electronic structure and x-ray absorption spectroscopy of TiO2 and LiTi2O4Manuscript (Other academic)
  • 8.
    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)
  • 9.
    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.

  • 10.
    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.

  • 11.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Lebègue, Sebastien
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Arnaud, B.
    Alouani, M.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Electronic and optical properties of MgH2: a first-principle GW investigation2005In: Journal of Applied Physics, ISSN 0021-8979, Vol. 98, no 9, p. 096106-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of MgH2 is studied using the state of the art all-electron projector-augmented-wave GW approximation. Both the ground-state and the high-pressure transformations are considered in this investigation. We have found an indirect (direct) band-gap of 5.58 eV (6.52 eV) for α-MgH2, which has a good agreement with the experimental findings. For the γ- and β-phases, we have found indirect (direct) band-gap values of 5.24 eV (5.33 eV) and 3.90 eV (4.72 eV), respectively. The optical properties are investigated by means of the complex dielectric function, which is calculated within the framework of a full-potential linearized augmented plane wave method and corrected by scissor operators. All phases are found to be color neutral insulators.

  • 12.
    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.

  • 13. Banerjee, Rudra
    et al.
    Banerjee, Mitali
    Majumdar, A. K.
    Mookerjee, Abhijit
    Sanyal, Biplab
    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.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nigam, A. K.
    Fe3.3Ni83.2Mo13.5: a likely candidate to show spin-glass behaviour at low temperatures2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 10, p. 106002-Article in journal (Refereed)
    Abstract [en]

    Unlike other transition metals alloyed with a non-magnetic metal, alloys of Ni behave rather differently. This is because of the fragility of the local magnetic moment on Ni. NiMo and NiW do not show any spin-glass phase. However, addition of Fe can bolster the moment on Ni. We wish to study whether the alloy Fe3.3Ni83.2Mo13.5, chosen near a composition where mean-field estimates suggest there could be a spin-glass phase, shows such a phase or not.

  • 14. Baranovskiy, A. E.
    et al.
    Grechnev, G. E.
    Fil, V. D.
    Ignatova, T. V.
    Logosha, A. V.
    Panfilov, A. S.
    Svechkarev, I. V.
    Shitsevalova, N. Y.
    Filippov, V. B.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Electronic structure, bulk and magnetic properties of MB6 and MB12 borides2007In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 442, no 1-2, p. 228-230Article in journal (Refereed)
    Abstract [en]

    The bulk and magnetic properties of MB6 and MB12 were investigated on the basis of first principles electronic structure calculations. The elastic constants were measured for ZrB12, HoB12, ErB12, TmB12, LuB12, YB6 and LaB6 compounds at low temperatures. The calculated equations of states and balanced crystal orbital overlap populations have allowed to analyse bonding and magnetic properties of MB6 and MB12

    .

  • 15. Baranovskiy, A.E.
    et al.
    Grechnev, G.E.
    Logosha, A.V.
    Svechkarev, I.V.
    Filippov, V.B.
    Shitsevalova, N. Yu.
    Zogal, O.J.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk magnetism.
    Electronic spectra and magnetic properties of RB6, RB12 and RB2C2 borides2006In: Physica Status Solidi C, Vol. 3, no 1, p. 229-232Article in journal (Refereed)
  • 16.
    Baranovskiy, A.E.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. TEORETISK MAGNETISM.
    Grechnev, G.E.
    Svechkarev, I.V.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk magnetism.
    Electronic structure and magnetic properties of GdM$_2$ compounds2003In: Journal of Magnetism and Magnetic Materials, Vol. 258, p. 520-Article in journal (Refereed)
    Abstract [en]

    Electronic structure calculations are carried out for the ferromagnetic GdM2 compounds (M=Mg, Al, Fe, Co, Ni, Rh, Ir, Pt). By using the calculated susceptibilities, densities of electronic states, and exchange parameters, the Curie temperatures were evaluated for these compounds in the framework of a modified molecular-field approach. The calculated magnetic ordering temperatures appeared to be in improved agreement with experimental data, in contrast to the results obtained within a conventional mean-field theory.

  • 17. Ben Romdhane, Ferdaous
    et al.
    Cretu, Ovidiu
    Debbichi, Lamjed
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lebegue, Sebastien
    Banhart, Florian
    Quasi-2D Cu2S Crystals on Graphene: In-situ Growth and ab-initio Calculations2015In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 11, no 11, p. 1253-1257Article in journal (Refereed)
    Abstract [en]

    Two-dimensional crystals of beta-copper sulfide are synthesized in an in-situ electron microscopy experiment. Copper crystals are deposited on an amorphous carbon film containing sulfur. The carbon film graphitizes upon heating and electron irradiation and allows the reaction of Cu and S towards two-dimensional Cu2S crystals. These are energetically favourable and bonded via van der Waals interactions to the graphitic substrate.

  • 18.
    Bengone, Olivier
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. teoretisk magnetism.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. teoretisk magnetism.
    et al.,
    Electronic structure and transport properties of CrAs/GaAs/CrAs multilayers from first principles theory2004In: phys rev b, Vol. 70, p. 35302-Article in journal (Refereed)
  • 19. Bengone, Olivier
    et al.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Kondenserade Materiens teori.
    Mirbt, Susanne
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Kondenserade Materiens teori.
    Origin of the negative GMR effects in Cr_xCo_1-x/cu/Co (111) trilayers2004In: Physical Review B, Vol. 69, p. 092406-Article in journal (Refereed)
  • 20.
    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%.

  • 21.
    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.

  • 22.
    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.

  • 23.
    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.

  • 24.
    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.

  • 25.
    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.

  • 26.
    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.

  • 27. 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.

  • 28.
    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)
  • 29.
    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)
  • 30.
    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.

  • 31.
    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)
  • 32.
    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.

  • 33.
    Bergqvist, Lars
    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, Theoretical Magnetism.
    Theory of weakly coupled two-dimensional magnets2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 20, p. 4853-Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the experimental findings of the magnetic properties of the weakly coupled trilayer system Ni4/CuN/Co2are reproduced by a theory that combines first principles calculations of the exchange interactions in a classical Heisenberg model with Monte Carlo simulations. Through an analysis of the spin–spin correlation function we show that two distinct temperatures can be identified; a higher temperature where long range magnetic order disappears and a lower temperature where the spin–spin correlation of the Ni atoms undergoes a drastic change. We argue that our findings hold in general for 'weak exchange link' systems.

  • 34.
    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.

  • 35.
    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
    Korzhavyi, Pavel
    Turek, Ilja
    Magnetic percolation in diluted magnetic semiconductors2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 13, p. 137202-Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the magnetic properties of diluted magnetic semiconductors are dominated by short ranged interatomic exchange interactions that have a strong directional dependence. By combining first principles calculations of interatomic exchange interactions with a classical Heisenberg model and Monte Carlo simulations, we reproduce the observed critical temperatures of a broad range of diluted magnetic semiconductors. We also show that agreement between theory and experiment is obtained only when the magnetic atoms are randomly positioned. This suggests that the ordering of diluted magnetic semiconductors is heavily influenced by magnetic percolation, and that the measured critical temperatures should be very sensitive to details in the sample preparation, in agreement with observations.

  • 36.
    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)
  • 37. 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.

  • 38. Bernien, M.
    et al.
    Miguel, J.
    Weis, C.
    Ali, Md. E.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Kurde, J.
    Krumme, B.
    Panchmatia, P. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Sanyal, B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Piantek, M.
    Srivastava, P.
    Baberschke, K.
    Oppeneer, Peter M.
    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.
    Kuch, W.
    Wende, H.
    Tailoring the Nature of Magnetic Coupling of Fe-Porphyrin Molecules to Ferromagnetic Substrates2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 4, p. 047202-Article in journal (Refereed)
    Abstract [en]

    We demonstrate that an antiferromagnetic coupling between paramagnetic Fe-porphyrin molecules and ultrathin Co and Ni magnetic films on Cu(100) substrates can be established by an intermediate layer of atomic oxygen. The coupling energies have been determined from the temperature dependence of x-ray magnetic circular dichroism measurements. By density functional theory+U calculations the coupling mechanism is shown to be superexchange between the Fe center of the molecules and Co surface-atoms, mediated by oxygen.

  • 39. 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.

  • 40.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panchmatia, Pooja M.
    Brumboiu, Iulia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bernien, Matthias
    Weis, Claudia
    Krumme, Bernhard
    Etz, Corina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kuch, Wolfgang
    Wende, Heiko
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Manipulation of spin state of iron porphyrin by chemisorption on magnetic substrates2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 2, p. 024401-Article in journal (Refereed)
    Abstract [en]

    One of the key factors behind the rapid evolution of molecular spintronics is the efficient realization of spin manipulation of organic molecules with a magnetic center. The spin state of such molecules may depend crucially on the interaction with the substrate on which they are adsorbed. In this paper we demonstrate, using ab initio density functional calculations, that the stabilization of a high spin state of an iron porphyrin (FeP) molecule can be achieved via chemisorption on magnetic substrates of different species and orientations, viz., Co(001), Ni(001), Ni(110), and Ni(111). The signature of chemisorption of FeP on magnetic substrates is evident from broad features in N K x-ray absorption (XA) and Fe L-2,L-3 x-ray magnetic circular dichroism (XMCD) measurements. Our theoretical calculations show that the strong covalent interaction with the substrate increases Fe-N bond lengths in FeP and hence a switching to a high spin state (S = 2) from an intermediate spin state (S = 1) is achieved. Due to chemisorption, ferromagnetic exchange interaction is established through a direct exchange between Fe and substrate magnetic atoms as well as through an indirect exchange via the N atoms in FeP. The mechanism of exchange interaction is further analyzed by considering structural models constructed from ab initio calculations. Also, it is found that the exchange interaction between Fe in FeP and a Ni substrate is almost 4 times smaller than with a Co substrate. Finally, we illustrate the possibility of detecting a change in the molecular spin state by XMCD, Raman spectroscopy, and spin-polarized scanning tunneling microscopy.

  • 41.
    Bhandary, Sumanta
    et al.
    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.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Defect controlled magnetism in FeP/graphene/Ni(111)2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 3405-Article in journal (Refereed)
    Abstract [en]

    Spin switching of organometallic complexes by ferromagnetic surfaces is an important topic in the area of molecular nanospintronics. Moreover, graphene has been shown as a 2D surface for physisorption of molecular magnets and strain engineering on graphene can tune the spin state of an iron porphyrin (FeP) molecule from S = 1 to S = 2. Our ab initio density functional calculations suggest that a pristine graphene layer placed between a Ni(111) surface and FeP yields an extremely weak exchange interaction between FeP and Ni whereas the introduction of defects in graphene shows a variety of ferromagnetic and antiferromagnetic exchange interactions. Moreover, these defects control the easy axes of magnetization, strengths of magnetic anisotropy energies and spin-dipolar contributions. Our study suggests a new way of manipulating molecular magnetism by defects in graphene and hence has the potential to be explored in designing spin qubits to realize logic operations in molecular nanospintronics.

  • 42.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Eriksson, Olle
    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.
    Katsnelson, Mikhail I.
    Complex edge effects in zigzag graphene nanoribbons due to hydrogen loading2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 16, p. 165405-Article in journal (Refereed)
    Abstract [en]

    We have performed density-functional calculations as well as employed a tight-binding theory, to study the effect of passivation of zigzag graphene nanoribbons (ZGNR) by hydrogen. We show that each edge C atom bonded with 2 H atoms open up a gap and destroys magnetism for small widths of the nanoribbon. However, a re-entrant magnetism accompanied by a metallic electronic structure is observed from eight rows and thicker nanoribbons. The electronic structure and magnetic state are quite complex for this type of termination, with sp(3) bonded edge atoms being nonmagnetic whereas the nearest neighboring atoms are metallic and magnetic. We have also evaluated the phase stability of several thicknesses of ZGNR and demonstrate that sp(3) bonded edge atoms with 2 H atoms at the edge can be stabilized over 1 H atom terminated edge at high temperatures and pressures.

  • 43.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ghosh, Saurabh
    Herper, Heike
    Wende, Heiko
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Graphene as a Reversible Spin Manipulator of Molecular Magnets2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 25, p. 257202-Article in journal (Refereed)
    Abstract [en]

    One of the primary objectives in molecular nanospintronics is to manipulate the spin states of organic molecules with a d-electron center, by suitable external means. In this Letter, we demonstrate by first principles density functional calculations, as well as second order perturbation theory, that a strain induced change of the spin state, from S = 1 -> S = 2, takes place for an iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene lattice. The process is reversible in the sense that the application of tensile or compressive strains in the graphene lattice can stabilize FeP in different spin states, each with a unique saturation moment and easy axis orientation. The effect is brought about by a change in Fe-N bond length in FeP, which influences the molecular level diagram as well as the interaction between the C atoms of the graphene layer and the molecular orbitals of FeP.

  • 44.
    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.

  • 45.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Penazzi, Gabriele
    Univ Bremen, BCCMS, D-28359 Bremen, Germany..
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Frauenheim, Thomas
    Univ Bremen, BCCMS, D-28359 Bremen, Germany..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Controlling Electronic Structure and Transport Properties of Zigzag Graphene Nanoribbons by Edge Functionalization with Fluorine2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 36, p. 21227-21233Article in journal (Refereed)
    Abstract [en]

    In this work, we report a detailed study of the electronic structure and transport properties of mono- and difluorinated edges of zigzag graphene nanoribbons (ZGNR) using density functional theory (DFT). The calculated formation energies at 0 K indicate that the stability of the nanoribbons increases with the increase in the concentration of difluorinated edge C atoms along with an interesting variation of the energy gaps between 0.0 to 0.66 eV depending on the concentration. This gives a possibility of tuning the band gaps by controlling the concentration of F for terminating the edges of the nanoribbons. The DFT results have been reproduced by density functional tight binding method. Using the nonequilibrium Green functional method, we have calculated the transmission coefficients of several mono- and difluorinated ZGNR as a function of unit cell size and degree of homogeneous disorder caused by the random placement of mono and difluorinated C atoms at the edges.

  • 46.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Penazzi, Gabriele
    BCCMS, Universitat Bremen.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Frauenheim, Thomas
    BCCMS, Universitat Bremen.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Controlling electronic structure and transport properties of zigzag graphene nanoribbons by mono- and difluorinated edge functionalizationManuscript (preprint) (Other academic)
    Abstract [en]

    In this work, we report a detailed study of the electronic structure and transport properties of mono- and di-fluorinated edges of zigzag graphene nanoribbons (ZGNR) using density functional theory (DFT). The calculated formation energies at 0K indicate that the stability of the nanoribbons increases with the increase in the concentration of di-fluorinated edge C atoms along with an interesting variation of the energy gaps between 0.0 to 0.66 eV depending on the concentration. This gives a possibility of tuning the band gaps by controlling the concentration of F for terminating the edges of the nanoribbons. The DFT results have been reproduced by single band tight binding as well as density functional tight binding methods. Using non-equilibrium Green functional method, we have calculated the transmission coecients of several mono and di-fluorinated ZGNR as a function of unit cell size and degree of homogeneous disorder caused by the random placement of mono and di-fuorinated C atoms at the edges.

  • 47.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Vienna Univ Technol, Inst Solid State Phys, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria..
    Schueler, Malte
    Univ Bremen, Inst Theoret Phys, Otto Hahn Allee 1, D-28359 Bremen, Germany.;Univ Bremen, Bremen Ctr Computat Mat Sci, Falturm 1, D-28359 Bremen, Germany..
    Thunstroem, Patrik
    Vienna Univ Technol, Inst Solid State Phys, Wiedner Hauptstr 8-10, A-1040 Vienna, Austria..
    di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Brena, Barbara
    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 Physics.
    Wehling, Tim
    Univ Bremen, Inst Theoret Phys, Otto Hahn Allee 1, D-28359 Bremen, Germany.;Univ Bremen, Bremen Ctr Computat Mat Sci, Falturm 1, D-28359 Bremen, Germany..
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Correlated electron behavior of metal-organic molecules: Insights from density functional theory combined with many-body effects using exact diagonalization2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 15, article id 155158Article in journal (Refereed)
    Abstract [en]

    A proper theoretical description of the electronic structure of the 3d orbitals in the metal centers of functional metalorganics is a challenging problem. We apply density functional theory and an exact diagonalization method in a many-body approach to study the ground-state electronic configuration of an iron porphyrin (FeP) molecule. Our study reveals that the consideration of multiple Slater determinants is important, and FeP is a potential candidate for realizing a spin crossover due to a subtle balance of crystal-field effects, on-site Coulomb repulsion, and hybridization between the Fe-d orbitals and ligand N-p states. The mechanism of switching between two close-lying electronic configurations of Fe-d orbitals is shown. We discuss the generality of the suggested approach and the possibility to properly describe the electronic structure and related low-energy physics of the whole class of correlated metal-centered organometallic molecules.

  • 48.
    Bhandary, Sumanta
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wehling, Tim
    Institute for Theoretical Physics, University of Bremen.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Correlated electron behavior of metalorganic molecules: insights from density functional theory and exact diagonalization studies.Manuscript (preprint) (Other academic)
    Abstract [en]

    The proper description of electronic structure of correlated orbitals in the metal centers of functional metalorganics is a challenging problem. In this letter, we apply density functional theory and exact diagonalization method in a many body approach to study the ground state electronic conguration of iron porphyrin (FeP) molecule. Our study reveals that FeP is a potential candidate for realizing a spin crossover due to a subtle balance of crystal elds and hybridization of the Fe d-orbitals and ligand N p-states. Moreover, the mechanism of switching between two close lying electronic congurations of Fe-d orbitals is revealed. This hybrid method can generally be applied to properly describe the electronic and related low energy physics of the whole class of correlated metal centered organometallic molecules.

  • 49.
    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.

  • 50.
    Bhattacharjee, Satadeep
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Rudra
    Wende, Heiko
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic structure of Co-phthalocyanine calculated by GGA plus U and hybrid functional methods2010In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 377, no 1-3, p. 96-99Article in journal (Refereed)
    Abstract [en]

    Electronic structure calculations have been performed for the Co-phthalocyanine molecule using density functional theory (DFT) within the framework of Generalized Gradient Approximation (GGA). The electronic correlation in Co 3d orbitals is treated in terms of the GGA+U method in the framework of the Hubbard model. We find that for U = 6 eV, the calculated structural parameters as well as the spectral features are in good agreement with the experimental findings. From our calculation both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are dominated by the pyrrole carbon, with a HOMO-LUMO gap of about 1.4 eV. The GGA+U results obtained with U = 6 eV compare reasonably well with the calculations performed using Gaussian basis set and hybrid functionals in terms of ground state geometry, spin state and spectral features. The calculated valence band photoemission spectrum is in quite good agreement with the recently published experimental results.

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