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Simulation of a spin-wave instability from atomistic spin dynamics
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2009 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 79, no 18, 184426- p.Article in journal (Refereed) Published
Abstract [en]

We study the spin dynamics of a Heisenberg model at finite temperature in the presence of an external fieldor a uniaxial anisotropy. For the case of the uniaxial anisotropy, our simulations show that the macromomentpicture breaks down. An effect which we refer to as a spin-wave instability results in a nondissipative Bloch-Bloembergen-type relaxation of the macromoment where the size of the macromoment changes and can evenbe made to disappear. This relaxation mechanism is studied in detail by means of atomistic spin dynamics simulations.

Place, publisher, year, edition, pages
2009. Vol. 79, no 18, 184426- p.
Keyword [en]
ferromagnetic relaxation, ferromagnetic resonance, Heisenberg model, magnetic anisotropy, magnetic moments, spin dynamics, spin waves
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-120101DOI: 10.1103/PhysRevB.79.184426ISI: 000266501200079OAI: oai:DiVA.org:uu-120101DiVA: diva2:302504
Available from: 2010-03-07 Created: 2010-03-07 Last updated: 2012-03-26Bibliographically approved
In thesis
1. Atomistic Spin Dynamics, Theory and Applications
Open this publication in new window or tab >>Atomistic Spin Dynamics, Theory and Applications
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The topic of this Thesis is magnetization dynamics on atomic length scales. A computational scheme, Atomistic Spin Dynamics, based on density functional theory, the adiabatic approximation and the atomic moment approximation is presented. Simulations are performed for chemically disordered systems, antiferromagnets and ferrimagnets and also systems with reduced dimensionality

The autocorrelation function of the archetypical spin glass alloy CuMn is sampled in simulations following a quenching protocol. The aging regime can be clearly identified and the dependence of the relaxation on the damping parameter is investigated. The time evolution of pair correlation and autocorrelation functions has been studied in simulations of the dilute magnetic semiconductor GaMnAs. The dynamics reveal a substantial short ranged magnetic order even at temperatures at or above the ordering temperature. The dynamics for different concentrations of As antisites are discussed.

Antiferromagnets offer opportunities for ultrafast switching, this is studied in simulations of an artificial antiferromagnet. For the right conditions, the cooperative effect of applied field torque and and the torque from the other sublattice enables very fast switching. The dynamics of bcc Fe precessing in a strong uniaxial anisotropy are investigated. It is demonstrated that the magnetization can shrink substantially due to a spin wave instability. The dynamics of a two-component model ferrimagnet at finite temperature are investigated. At temperatures where the magnetic system is close to the magnetic and angular momentum compensations points of the ferrimagnet, the relaxation in a uniaxial easy exis anisotropy resembles results in recent experiments on ferrimagnetic resonance.

The different cases of uniaxial or colossal magnetic anisotropy in nanowires at different temperatures are compared. The magnon softening in a ferromagnetic monolayer is investigated, giving results that compare well with recent experiments. The effect of lattice relaxation can be treated in first principles calculations. Subsequent simulations captures the softening of magnons caused by reduced dimensionality and temperature.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 108 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 776
Keyword
ab initio calculations, spin dynamics, magnetization, magnetic switching, diluted magnetic semiconductors, spin glasses, ferromagnetic relaxation, ferrimagnets, antiferromagnets
National Category
Condensed Matter Physics Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-120103 (URN)978-91-554-7921-3 (ISBN)
Public defence
2010-12-03, Polhemsalen, Ångström laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 706Available from: 2010-11-11 Created: 2010-03-07 Last updated: 2011-03-21Bibliographically approved

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Nordström, LarsEriksson, Olle

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