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Role of magnetic impurities in Fe/V multilayers
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, Theoretical Magnetism.
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 14, 144408- p.Article in journal (Refereed) 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.

Place, publisher, year, edition, pages
2008. Vol. 77, no 14, 144408- p.
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-96087DOI: 10.1103/PhysRevB.77.144408ISI: 000255457300043OAI: oai:DiVA.org:uu-96087DiVA: diva2:170549
Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2017-12-14Bibliographically approved
In thesis
1. A Theoretical Study of Magnetism in Nanostructured Materials
Open this publication in new window or tab >>A Theoretical Study of Magnetism in Nanostructured Materials
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. x + 78 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 167
Keyword
Physics, magnetism, clusters, non-collinear, multilayers, first-principles theory, electronic structure, high-moment materials, exchange interactions, linear scaling methods, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-6763 (URN)91-554-6527-7 (ISBN)
Public defence
2006-05-05, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2012-03-27Bibliographically approved
2. Spin Dynamics and Magnetic Multilayers
Open this publication in new window or tab >>Spin Dynamics and Magnetic Multilayers
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Theoretical studies based on first-principles theory are presented for a number of different magnetic systems. The first part of the thesis concerns spin dynamics and the second part concerns properties of magnetic multilayers. The theoretical treatment is based on electronic structure calculations performed by means of density functional theory.

A method is developed for simulating atomistic spin dynamics at finite temperatures, which is based on solving the equations of motion for the atomic spins by means of Langevin dynamics. The method relies on a mapping of the interatomic exchange interactions from density functional theory to a Heisenberg Hamiltonian. Simulations are performed for various magnetic systems and processes beyond the reach of conventional micromagnetism. As an example, magnetization dynamics in the limit of large magnetic and anisotropy fields is explored. Moreover, the method is applied to studying the dynamics of systems with complex atomic order such as the diluted magnetic semiconductor MnGaAs and the spin glass alloy CuMn. The method is also applied to a Fe thin film and a Fe/Cr/Fe trilayer system, where the limits of ultrafast switching are explored. Current induced magnetization dynamics is investigated by calculating the current induced spin-transfer torque by means of density functional theory combined with the relaxation time approximation and semi-classical Boltzmann theory. The current induced torque is calculated for the helical spin-density waves in Er and fcc Fe, where the current is found to promote a rigid rotation of the magnetic order.

Properties of magnetic multilayers composed of magnetic and nonmagnetic layers are investigated by means of the Korringa-Kohn-Rostocker interface Green's function method. Multilayer properties such as magnetic moments, interlayer exchange coupling and ordering temperatures are calculated and compared with experiments, with focus on understanding the influence of interface quality. Moreover, the influence on the interlayer exchange coupling of alloying the nonmagnetic spacer layers with small amounts of a magnetic impurity is investigated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. x, 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 326
Keyword
Physics, magnetism, electronic structure, density functional theory, spin dynamics, spin-transfer torque, spin-density wave, multilayer, interface structure, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-8168 (URN)978-91-554-6944-3 (ISBN)
Public defence
2007-09-21, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15
Opponent
Supervisors
Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2012-03-28Bibliographically approved

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Bergman, AndersEriksson, Olle

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