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Spin-Transfer Torque in Helical Spin Density Waves
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 10, 104433- p.Article in journal (Refereed) Published
Abstract [en]

The current driven magnetization dynamics of a helical spin-density wave is investigated. Expressions for calculating the spin-transfer torque of real systems from first-principles density-functional theory are presented. These expressions are used for calculating the   spin-transfer torque for the spin spirals of Er and fcc Fe at two different lattice volumes. It is shown that the calculated torque induces a rigid rotation of the order parameter with respect to the spin spiral axis. The torque is found to depend on the wave vector of the spin spiral and the spin polarization of the Fermi surface states. The resulting dynamics of the spin spiral is also discussed.

Place, publisher, year, edition, pages
2009. Vol. 79, no 10, 104433- p.
Keyword [en]
density functional theory, electron spin polarisation, erbium, Fermi surface, ferromagnetic materials, iron, magnetisation, spin density waves
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96084DOI: 10.1103/PhysRevB.79.104433ISI: 000264768600089OAI: oai:DiVA.org:uu-96084DiVA: diva2:170546
Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2017-12-14Bibliographically approved
In thesis
1. 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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Nordström, Lars

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