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Dynamics of diluted magnetic semiconductors from atomistic spin-dynamics simulations: Mn-doped GaAs
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
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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 14, 144419- p.Article in journal (Refereed) Published
Abstract [en]

The dynamical behavior of the magnetism of diluted magnetic semiconductors (DMSs) has been investigated by means of atomistic spin-dynamics simulations. The conclusions drawn from the study are argued to be general for DMS systems in the low-concentration limit, although all simulations are done for 5% Mn-doped GaAs with various concentrations of As antisite defects. The magnetization curve M(T) and the Curie temperature T-C have been calculated and are found to be in good correspondence to the results from Monte Carlo simulations and experiments. Furthermore, equilibrium and nonequilibrium behaviors of the magnetic pair-correlation function have been extracted. The dynamics of DMS systems reveals a substantial short-ranged magnetic order even at temperatures at or above the ordering temperature, with a nonvanishing pair-correlation function extending up to several atomic shells. For the high As antisite concentrations the simulations show a short-ranged antiferromagnetic coupling and a weakened long-ranged ferromagnetic coupling. For sufficiently large concentrations we do not observe any long-ranged ferromagnetic correlation. A typical dynamical response shows that starting from a random orientation of moments, the spin correlation develops very fast (similar to 1 ps) extending up to 15 atomic shells. Above similar to 10 ps in the simulations, the pair correlation is observed to extend over some 40 atomic shells. The autocorrelation function has been calculated and compared with ferromagnets such as bcc Fe and spin-glass materials. We find no evidence in our simulations for a spin-glass behavior for any concentration of As antisites. Instead the magnetic response is better described as slow dynamics, at least when compared to that of a regular ferromagnet such as bcc Fe.

Place, publisher, year, edition, pages
2008. Vol. 78, no 14, 144419- p.
National Category
Physical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-107071DOI: 10.1103/PhysRevB.78.144419ISI: 000260574300060OAI: oai:DiVA.org:uu-107071DiVA: diva2:227629
Available from: 2009-07-15 Created: 2009-07-15 Last updated: 2017-12-13
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)
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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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Hellsvik, JohanNordström, LarsSanyal, BiplabEriksson, OlleNordblad, PerSvedlindh, Peter

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