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Theory of the temperature dependence of the easy axis of magnetization in hcp Gd
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
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2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 9, 094423- p.Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
2005. Vol. 72, no 9, 094423- p.
Keyword [en]
MAGNETOCRYSTALLINE ANISOTROPY ENERGY, SPIN-DENSITY APPROXIMATION, GADOLINIUM METAL, SINGLE CRYSTALS, EASY DIRECTION, MAGNETISM
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-93067DOI: 10.1103/PhysRevB.72.094423OAI: oai:DiVA.org:uu-93067DiVA: diva2:166431
Available from: 2005-04-28 Created: 2005-04-28 Last updated: 2012-04-01Bibliographically approved
In thesis
1. Materials for Magnetic Recording Applications
Open this publication in new window or tab >>Materials for Magnetic Recording Applications
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the first part of this work, the influence of hydrogen on the structural and magnetic properties of Fe/V(001) superlattices was studied. The local structure of the vanadium-hydride layers was determined by extended x-ray absorption fine structure (EXAFS) measurements. The magnetic ordering in a weakly coupled Fe/V(001) superlattice was investigated using the magneto-optical Kerr effect (MOKE). The interlayer exchange coupling is weakened upon alloying with hydrogen and a phase with short-range magnetic order was observed.

The second part is concerned with first-principles calculations of magnetic materials, with a focus on magnetic recording applications. The uniaxial magnetic anisotropy energy (MAE) of Fe, Co, and Ni was calculated for tetragonal and trigonal structures. Based on an analysis of the electronic states of tetragonal Fe and Co at the center of the Brillouin zone, tetragonal Fe-Co alloys were proposed as a material that combines a large uniaxial MAE with a large saturation magnetization. This was confirmed by experimental studies on (Fe,Co)/Pt superlattices. The large uniaxial MAE of L10 FePt is caused by the large spin-orbit interaction on the Pt sites in connection with a strong hybridization between Fe and Pt. Furthermore, it was shown that the uniaxial MAE can be increased by alloying the Fe sublattice with Mn. The combination of the high-moment rare-earth (RE) metals with the high-TC 3d transition metals in RE/Cr/Fe multilayers (RE = Gd, Tb, Dy) gives rise to a strong ferromagnetic effective exchange interaction between the Fe layers and the RE layer. The MAE of hcp Gd was found to have two principal contributions, namely the dipole interaction of the large localized 4f spins and the band electron magnetic anisotropy due to the spin-orbit interaction. The peculiar temperature dependence of the easy axis of magnetization was reproduced on a qualitative level.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. viii + 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 53
Keyword
Physics, magnetic materials, magnetic anisotropy, saturation magnetization, magnetic data storage, superlattice, hydrogen, density functional theory, first-principles calculations, two-dimensional magnetism, FP-LMTO, EXAFS, MOKE, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-5800 (URN)91-554-6252-9 (ISBN)
Public defence
2005-05-20, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2005-04-28 Created: 2005-04-28 Last updated: 2011-05-05Bibliographically approved

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Burkert, TillEriksson, OlleNordström, LarsBrooks, Michael S. S.

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