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Author Suhl, Harry
Sponsorship (US)
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Publisher The American Physical Society
Language English
Subject Keyword CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS ♦ DEGREES OF FREEDOM ♦ FERROMAGNETIC RESONANCE ♦ MAGNETIC MOMENTS ♦ MAGNETIZATION ♦ OCCUPATION NUMBER ♦ VALENCE ♦ VECTORS
Abstract In micromagnetics, it is common practice to describe the motion of the magnetization vector in terms of the Landau{endash}Liftshitz{endash}Gilbert equations. In these, the strength of the dissipative torque is measured by a phenomenological parameter, and the form of the torque is chosen so as to lead to a reversion of the magnetic vector to a stable or metastable position. The microscopic origin of the parameter, as well as the correct form of the torque is not generally discussed. Retaining the mathematical description of all the degrees of freedom to which the magnetization vector is coupled, would give correct results. However, it is obviously desirable to formally eliminate these degrees of freedom, resulting in equations for the magnetization vector alone. In this article, the necessary procedure is carried out for the particular case in which the loss mechanism arises from valence fluctuations changing electron occupation numbers, and thereby the magnetic moments, of the various sites. Since the fluctuations are not instantaneous, the total magnetization vector develops time lags that manifest themselves as a loss mechanism. Apart from a numerical measure of this damping, we find that the structure of the torque term does not, in general, have one of the familiar forms. Furthermore, this results in certain changes in the switching characteristics of small magnetic particles. This particular origin of dissipation was discussed in the early 1950{close_quote}s by Clogston, Gate, and others in the context of domain wall motion and small-signal ferromagnetic resonance, but no attempt was made at that time to re-express the entire process in terms of an equation of motion of the magnetization vector alone. {copyright} 2001 American Institute of Physics.
ISSN 00218979
Educational Use Research
Learning Resource Type Article
Publisher Date 2001-06-01
Publisher Place United States
Journal Journal of Applied Physics
Volume Number 89
Issue Number 11


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