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Magnetic anisotropy and evolution of ground-state domain structures in bcc Fe81Ni19/Co(001) superlattices
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
Institute of Theoretical Physics, University of Hamburg, 20355 Hamburg, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
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2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 2, 024421- p.Article in journal (Refereed) Published
Abstract [en]

The magnetic anisotropy and evolution of striped magnetic domain structures in bcc Fe81Ni19/Co(001) superlattices with the total thickness ranging from 85 to 1370 nm has been studied by magneto-optical Kerr effect and magnetic force microscopy. At a thickness of about 85 nm [25 bilayers (BL)] the domains appear as stripe domains, typical for perpendicular anisotropy films, with the weak cubic anisotropy of the in-plane magnetization component stabilizing the stripe direction. The magnetic domain period strongly depends on the thickness of the superlattice. As the thickness increases, the equilibrium magnetization orients at oblique angles with respect to the film plane and continuously varies with the thickness from in-plane to out-of-plane. We first apply a simple phenomenological model which correctly predicts the transition from in-plane to out-of-plane magnetization as well as increasing domain period and saturation field with increasing BL number. The results indicate the presence of partial flux-closure domains at the film surface with the tilt angle continuously varying with the superlattice thickness. By solving a linearized Landau–Lifshitz equation together with Maxwell’s equations in magnetostatic approximation for samples consisting of up to 1000 individual layers, we calculate the spin-wave dispersion and determine the stability conditions for the saturated ferromagnetic state. From these results the dependence of the saturation field on the number of layers is inferred and agrees well with the experiment. The uniaxial bulk anisotropy is attributed to distortions along the c axis and the results further show evidence for the presence of an easy-plane interface anisotropy in these samples.

Place, publisher, year, edition, pages
The American Physical Society , 2008. Vol. 78, no 2, 024421- p.
Keyword [en]
Domain effects, magnetization curves, and hysteresis, Magnetic properties of thin films, surfaces, and interfaces, Magnetic properties of nanostructures
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-119892DOI: 10.1103/PhysRevB.78.024421ISI: 000258190200080OAI: oai:DiVA.org:uu-119892DiVA: diva2:301212
Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2012-03-15Bibliographically approved
In thesis
1. Density Functional Theory Applied to Materials for Spintronics
Open this publication in new window or tab >>Density Functional Theory Applied to Materials for Spintronics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The properties of dilute magnetic semiconductors have been studied by combined ab initio, Monte Carlo, and experimental techniques. This class of materials could be very important for future spintronic devices, that offer enriched functionality by making use of both the spin and the charge of the electrons. The main part of the thesis concerns the transition metal doped ZnO.

The role of defects on the magnetic interactions in Mn-doped ZnO was investigated. In the presence of acceptor defects such as zinc vacancies and oxygen substitution by nitrogen, the magnetic interactions are ferromagnetic. For dilute concentrations of Mn (~ 5%) the ordering temperature of the system is low, due to the short ranged character of the exchange interactions and disorder effects.

The clustering tendency of the Co atoms in a ZnO matrix was also studied. The electronic structure, and in turn the magnetic interactions among the Co atoms, is strongly dependent on the exchange-correlation functional used. It is found that Co impurities tend to form nanoclusters and that the interactions among these atoms are antiferromagnetic within the local spin density approximation + Hubbard U approach.

The electronic structure, as well as the chemical and magnetic interactions in Co and (Co,Al)-doped ZnO, was investigated by joined experimental and theoretical techniques. For a good agreement between the two, approximations beyond the local density approximation must be used. It is found that the Co atoms prefer to cluster within the semiconducting matrix, a tendency which is increased with Al co-doping. We envision that it is best to describe the system as superparamagnetic due to the formation of  Co nanoclusters within which the interactions are antiferromagnetic.

The magnetic anisotropy and evolution of magnetic domains in Fe81Ni19/Co(001) superlattices were investigated both experimentally, as well as using model spin dynamics. A magnetic reorientation transition was found.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 67 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 721
spintronics, dilute magnetic semiconductors, density functional theory, exchange interactions, magnetic percolation, ordering temperature, disorder, electronic structure
National Category
Physical Sciences
Research subject
Materials Science
urn:nbn:se:uu:diva-119887 (URN)978-91-554-7737-0 (ISBN)
Public defence
2010-04-16, Polhemsalen, 751 20 Uppsala, Ångström Laboratory, 10:15 (English)
Available from: 2010-03-26 Created: 2010-03-02 Last updated: 2010-03-26Bibliographically approved

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Publisher's full texthttp://link.aps.org/doi/10.1103/PhysRevB.78.024421

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Soroka, I. L.Eriksson, OlleHjörvarsson, Björgvin
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