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  • 201. Belonoshko, Anatoly B.
    et al.
    Rosengren, Anders
    Burakovsky, Leonid
    Preston, L
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Melting of Fe and Fe0.9375Si0.0625 at Earth's core pressures studied using ab initio molecular dynamics2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 22, s. 220102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The issue of melting of pure iron and iron alloyed with lighter elements at high pressure is critical to the physics of the Earth. The iron melting curve in the relevant pressure range between 3 and 4 Mbar is reasonably well established from the theoretical point of view. However, so far no one attempted a direct atomistic simulation of iron alloyed with light elements. We investigate here the impact of alloying the body-centered cubic (bcc) Fe with Si. We simulate melting of the bcc Fe and Fe0.9375Si0.0625 alloy by ab initio molecular dynamics. The addition of light elements to the hexagonal-close-packed (hcp) iron is known to depress its melting temperature (T-m). We obtain, in marked contrast, that alloying of bcc Fe with Si does not lead to T-m depression; on the contrary, the T-m slightly increases. This suggests that if Si is a typical impurity in the Earth's inner core, then the stable phase in the core is bcc rather than hcp.

  • 202. Belonoshko, Anatoly B.
    et al.
    Skorodumova, Natalia V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Davis, Sergio
    Osiptsov, Alexander N.
    Rosengren, Anders
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Origin of the low rigidity of the Earth's inner core2007Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, nr 5831, s. 1603-1605Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Earth's solid-iron inner core has a low rigidity that manifests itself in the anomalously low velocities of shear waves as compared to shear wave velocities measured in iron alloys. Normally, when estimating the elastic properties of a polycrystal, one calculates an average over different orientations of a single crystal. This approach does not take into account the grain boundaries and defects that are likely to be abundant at high temperatures relevant for the inner core conditions. By using molecular dynamics simulations, we show that, if defects are considered, the calculated shear modulus and shear wave velocity decrease dramatically as compared to those estimates obtained from the averaged single-crystal values. Thus, the low shear wave velocity in the inner core is explained.

  • 203. Belonoshko, Anatoly B.
    et al.
    Skorodumova, Natalia V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Rosengren, Anders
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Elastic anisotropy of Earth's inner core2008Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 319, nr 5864, s. 797-800Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Earth's solid- iron inner core is elastically anisotropic. Sound waves propagate faster along Earth's spin axis than in the equatorial plane. This anisotropy has previously been explained by a preferred orientation of the iron alloy hexagonal crystals. However, hexagonal iron becomes increasingly isotropic on increasing temperature at pressures of the inner core and is therefore unlikely to cause the anisotropy. An alternative explanation, supported by diamond anvil cell experiments, is that iron adopts a body- centered cubic form in the inner core. We show, by molecular dynamics simulations, that the body- centered cubic iron phase is extremely anisotropic to sound waves despite its high symmetry. Direct simulations of seismic wave propagation reveal an anisotropy of 12%, a value adequate to explain the anisotropy of the inner core.

  • 204. Belonoshko, Anatoly
    et al.
    Rosengren, Anders
    Skorodumova, Natalia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik IV.
    Bastea, S
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik IV.
    Smearing of shock front in liquid deuterium at high impact velocities2005Ingår i: J.Chem.Phys., Vol. 122, s. 124503-Artikel i tidskrift (Refereegranskat)
  • 205. Belonoshko, Anatoly
    et al.
    Skorodumova, Natalia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik IV.
    Rosengren, Anders
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik IV.
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik IV.
    Burakovsky, Leonid
    Preston, D. L.
    High-pressure melting of MgSiO32005Ingår i: Phys. Rev. Lett.,, Vol. 94, s. 195701-Artikel i tidskrift (Refereegranskat)
  • 206. Belonoshko, Anatoly
    et al.
    Skorodumova, Natalia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Rosengren, Anders
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Melting and critical superheating2006Ingår i: Phys. Rev. B, Vol. 73, s. 012201-Artikel i tidskrift (Refereegranskat)
  • 207.
    Bengone, Olivier
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik IV. teoretisk magnetism.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik IV. teoretisk magnetism.
    et al.,
    Electronic structure and transport properties of CrAs/GaAs/CrAs multilayers from first principles theory2004Ingår i: phys rev b, Vol. 70, s. 35302-Artikel i tidskrift (Refereegranskat)
  • 208. Bengone, Olivier
    et al.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik IV. Kondenserade Materiens teori.
    Mirbt, Susanne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik IV. Kondenserade Materiens teori.
    Origin of the negative GMR effects in Cr_xCo_1-x/cu/Co (111) trilayers2004Ingår i: Physical Review B, Vol. 69, s. 092406-Artikel i tidskrift (Refereegranskat)
  • 209.
    Bergersen, Henrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik V.
    Abu-samba, M.
    Harnes, J.
    Björneholm, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik V.
    Svensson, Svante
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik V.
    Saethre, L. J.
    Börve, K. J.
    Size of neutral argon clusters from core-level photoelectron spectroscopy2006Ingår i: Physical Chemistry Chemical Physics, Vol. 16, s. 1891-Artikel i tidskrift (Refereegranskat)
  • 210.
    Bergersen, Henrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Abu-samha, M.
    Lindblad, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Marinho, Ricardo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Céolin, Denis
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Öhrwall, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Sæthre, L. J.
    Tchaplyguine, M.
    Børve, K. J.
    Svensson, Svante
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Björneholm, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters2006Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 429, nr 1-3, s. 109-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Core-level photoelectron spectra of free neutral methane clusters have been recorded. These spectra exhibit well-resolved surface and bulk features as well as vibrational fine structure. The vibrational structure in the cluster signal is well reproduced by a theoretical model that assumes independent contributions from inter- and intramolecular modes. The intramolecular contribution to the vibrational line-shape is taken to be equal to that of the monomer in the gas phase, while the intermolecular part is simplified to line broadening. An estimate of the cluster size has been made on the basis of the observed surface-to-bulk intensity ratio.

  • 211.
    Bergersen, Henrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Abu-samha, M.
    Lindblad, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Marinho, Ricardo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Öhrwall, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Tchaplyguine, M.
    Børve, K. J.
    Svensson, Svante
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Björneholm, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Two size regimes of methanol clusters produced by adiabatic expansion2006Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, nr 18, s. 184303-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Free neutral methanol clusters produced by adiabatic expansion have been studied by photoelectron spectroscopy and line shape modeling. The results show that clusters belonging to two distinct size regimes can be produced by changing the expansion conditions. While the larger size regime can be well described by line shapes calculated for clusters consisting of hundreds of molecules, the smaller size regime corresponds to methanol oligomers, predominantly of cyclic structure. There is little contribution from dimers to the spectra.

  • 212.
    Bergersen, Henrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Marinho, R. R. T.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Pokapanich, Wandared
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Björneholm, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Sæthre, L. J.
    Department of Chemistry, University of Bergen.
    Lindblad, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    Öhrwall, Gunnar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik V.
    A photoelectron spectroscopic study of aqueous tetrabutylammonium iodide2007Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, nr 32, s. 326101-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Photoelectron spectra of tetrabutylammonium iodide (TBAI) dissolved in water have been recorded using a novel experimental set-up, which enables photoelectron spectroscopy of volatile liquids. The set-up is described in detail. Ionization energies are reported for I 5p, I 4d, C 1s and N 1s. The C 1s spectrum shows evidence of inelastic scattering of the photoelectrons, that differs from the case of TBAI in formamide.

  • 213.
    Bergman, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    A Theoretical Study of Magnetism in Nanostructured Materials2006Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

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

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

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

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

    Delarbeten
    1. Linear scaling density matrix approach for the linear muffin-tin orbital method
    Öppna denna publikation i ny flik eller fönster >>Linear scaling density matrix approach for the linear muffin-tin orbital method
    (Engelska)Manuskript (Övrigt vetenskapligt)
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94286 (URN)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2012-03-14Bibliografiskt granskad
    2. Fermi-surface effect on magnetic interlayer coupling
    Öppna denna publikation i ny flik eller fönster >>Fermi-surface effect on magnetic interlayer coupling
    Visa övriga...
    2004 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 6, s. 064408-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94287 (URN)10.1103/PhysRevB.70.064408 (DOI)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    3. Role of magnetic impurities in Fe/V multilayers
    Öppna denna publikation i ny flik eller fönster >>Role of magnetic impurities in Fe/V multilayers
    2008 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 14, s. 144408-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-96087 (URN)10.1103/PhysRevB.77.144408 (DOI)000255457300043 ()
    Tillgänglig från: 2007-09-03 Skapad: 2007-09-03 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    4. Magnetism of Fe/V and Fe/Co multilayers
    Öppna denna publikation i ny flik eller fönster >>Magnetism of Fe/V and Fe/Co multilayers
    Visa övriga...
    2003 (Engelska)Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, nr 5, s. S599-S615Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94289 (URN)10.1088/0953-8984/15/5/313 (DOI)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    5. Magnetic properties of Fe/Co(001) superlattices from first-principles theory
    Öppna denna publikation i ny flik eller fönster >>Magnetic properties of Fe/Co(001) superlattices from first-principles theory
    Visa övriga...
    2006 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 17, s. 174409-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94290 (URN)10.1103/PhysRevB.74.174409 (DOI)000242409000080 ()
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    6. Local magnetic effects of interface alloying in Fe/Co multilayers
    Öppna denna publikation i ny flik eller fönster >>Local magnetic effects of interface alloying in Fe/Co multilayers
    Visa övriga...
    Ingår i: Journal of Physics: Condensed MatterArtikel i tidskrift (Refereegranskat) Submitted
    Identifikatorer
    urn:nbn:se:uu:diva-94291 (URN)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12Bibliografiskt granskad
    7. Magnetism of Fe clusters embedded in a Co matrix from first-principles theory
    Öppna denna publikation i ny flik eller fönster >>Magnetism of Fe clusters embedded in a Co matrix from first-principles theory
    Visa övriga...
    2004 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 17, s. 174446-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94292 (URN)10.1103/PhysRevB.70.174446 (DOI)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    8. Magnetic moments of Fe clusters embedded in an Fe-Co alloy
    Öppna denna publikation i ny flik eller fönster >>Magnetic moments of Fe clusters embedded in an Fe-Co alloy
    2006 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 10, s. 104422-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94293 (URN)10.1103/PhysRevB.74.104422 (DOI)000240872000066 ()
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    9. Conditions for noncollinear instabilities of ferromagnetic materials
    Öppna denna publikation i ny flik eller fönster >>Conditions for noncollinear instabilities of ferromagnetic materials
    Visa övriga...
    2004 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, nr 10, s. 107205-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94356 (URN)10.1103/PhysRevLett.93.107205 (DOI)
    Tillgänglig från: 2006-04-21 Skapad: 2006-04-21 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    10. Theoretical and experimental study of the magnetic structure of TlCo2Se2
    Öppna denna publikation i ny flik eller fönster >>Theoretical and experimental study of the magnetic structure of TlCo2Se2
    Visa övriga...
    2004 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 2, s. 024407-Artikel i tidskrift (Refereegranskat) Published
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94358 (URN)10.1103/PhysRevB.70.024407 (DOI)
    Tillgänglig från: 2006-04-21 Skapad: 2006-04-21 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    11. Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0): Experiment and theory
    Öppna denna publikation i ny flik eller fönster >>Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0): Experiment and theory
    Visa övriga...
    2006 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 9, s. 094419-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Oorganisk kemi Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:uu:diva-82093 (URN)10.1103/PhysRevB.74.094419 (DOI)000240871700046 ()
    Tillgänglig från: 2006-09-18 Skapad: 2006-09-18 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    12. Magnetic structure of a small fcc Fe cluster in Cu
    Öppna denna publikation i ny flik eller fönster >>Magnetic structure of a small fcc Fe cluster in Cu
    (Engelska)Manuskript (Övrigt vetenskapligt)
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94297 (URN)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2012-03-26Bibliografiskt granskad
    13. Magnetic interactions of Mn clusters supported on Cu
    Öppna denna publikation i ny flik eller fönster >>Magnetic interactions of Mn clusters supported on Cu
    Visa övriga...
    (Engelska)Ingår i: Physical Review BArtikel i tidskrift (Refereegranskat) Submitted
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94298 (URN)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2012-03-26Bibliografiskt granskad
    14. Magnetic structure of Fe, Cr, and Mn clusters supported on Cu(111).
    Öppna denna publikation i ny flik eller fönster >>Magnetic structure of Fe, Cr, and Mn clusters supported on Cu(111).
    Visa övriga...
    (Engelska)Manuskript (Övrigt vetenskapligt)
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94299 (URN)
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2012-03-26Bibliografiskt granskad
    15. Non-collinear magnetisation of V clusters supported on a Cu (111) surface: Theory
    Öppna denna publikation i ny flik eller fönster >>Non-collinear magnetisation of V clusters supported on a Cu (111) surface: Theory
    Visa övriga...
    2006 (Engelska)Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 21, s. 4838-4842Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nyckelord
    density functional calculations, vanadium, metal-metal magnetic heterostructures
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94300 (URN)10.1016/j.susc.2006.08.004 (DOI)000242514400007 ()
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    16. Magnetism of Co overlayers and nanostructures on W(001): A first principles study
    Öppna denna publikation i ny flik eller fönster >>Magnetism of Co overlayers and nanostructures on W(001): A first principles study
    Visa övriga...
    2008 (Engelska)Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, nr 6, s. 1173-1179Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nyckelord
    density functional calculations, nanoclusters, metal-metal magnetic heterostructures
    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94301 (URN)10.1016/j.jmmm.2007.11.011 (DOI)000254416300066 ()
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    17. Spin and orbital moments of Fe clusters supported on Ni(001)
    Öppna denna publikation i ny flik eller fönster >>Spin and orbital moments of Fe clusters supported on Ni(001)
    Visa övriga...
    2008 (Engelska)Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, nr 1, s. 015001-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94302 (URN)10.1088/0953-8984/20/01/015001 (DOI)000252921800002 ()
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    18. A first-principles study of the magnetism and electronic structure of Cr clusters supported on a Au(111) surface
    Öppna denna publikation i ny flik eller fönster >>A first-principles study of the magnetism and electronic structure of Cr clusters supported on a Au(111) surface
    Visa övriga...
    2007 (Engelska)Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, nr 15, s. 156226-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

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

    Nationell ämneskategori
    Fysik
    Identifikatorer
    urn:nbn:se:uu:diva-94303 (URN)10.1088/0953-8984/19/15/156226 (DOI)000245670400032 ()
    Tillgänglig från: 2006-04-12 Skapad: 2006-04-12 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
  • 214.
    Bergman, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen. Institutionen för fysik och materialvetenskap, Fysik IV.
    High moment materials studied by real-space first principles theory2004Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 215.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Burkert, Till
    Sanyal, Biplab
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Frota-Pessôa, Sonia
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Ruban, Andrei.V.
    Simak, Sergei.I.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Magnetic properties of Fe/Co(001) superlattices from first-principles theory2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 17, s. 174409-Artikel i tidskrift (Refereegranskat)
    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%.

  • 216.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Magnetic moments of Fe clusters embedded in an Fe-Co alloy2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 10, s. 104422-Artikel i tidskrift (Refereegranskat)
    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.

  • 217.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Teoretisk magnetism.
    Holmström, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Teoretisk magnetism.
    Niklasson, A.M.N.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Kondenserade materiens teori (Fysik IV).
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Teoretisk magnetism.
    Magnetism of Fe clusters embedded in a Co matrix from first-principles theory2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 17, s. 174446-Artikel i tidskrift (Refereegranskat)
    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.

  • 218.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Holmström, Erik
    Niklasson, Anders M.N.
    Linear scaling density matrix approach for the linear muffin-tin orbital methodManuskript (Övrigt vetenskapligt)
  • 219.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Klautau, Angela B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    A first-principles study of the magnetism and electronic structure of Cr clusters supported on a Au(111) surface2007Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, nr 15, s. 156226-Artikel i tidskrift (Refereegranskat)
    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.

  • 220.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Teoretisk magnetism.
    Klautau, Angela B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Teoretisk magnetism.
    Non-collinear magnetisation of V clusters supported on a Cu (111) surface: Theory2006Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 600, nr 21, s. 4838-4842Artikel i tidskrift (Refereegranskat)
    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.

  • 221.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Klautau, Angela Burlamaqui
    Frota-Pessoa, Sonia
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Magnetic structures of small Fe, Mn, and Cr clusters supported on Cu(111): Noncollinear first-principles calculations2007Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 22, s. 224425-Artikel i tidskrift (Refereegranskat)
    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.

  • 222.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Klautau, Angela Burlamaqui
    Frota-Pessoa, Sonia
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Magnetism of Co overlayers and nanostructures on W(001): A first principles study2008Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, nr 6, s. 1173-1179Artikel i tidskrift (Refereegranskat)
    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.

  • 223. Bergman, Anders
    et al.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Teoretisk magnetism.
    Klautau, Angela Burlamaqui
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Teoretisk magnetism.
    Magnetic interactions of Mn clusters supported on Cu2006Ingår i: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 73, nr 17, s. 174434-Artikel i tidskrift (Refereegranskat)
    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.

  • 224.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Nordström, Lars
    Klautau, Angela.B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Magnetic interactions of Mn clusters supported on CuIngår i: Physical Review BArtikel i tidskrift (Refereegranskat)
  • 225.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Nordström, Lars
    Klautau, Angela.B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Magnetic structure of Fe, Cr, and Mn clusters supported on Cu(111).Manuskript (Övrigt vetenskapligt)
  • 226.
    Bergman, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Robles, Roberto
    Nordström, Lars
    Magnetic structure of a small fcc Fe cluster in CuManuskript (Övrigt vetenskapligt)
  • 227. Bergmark, T.
    et al.