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Rotation of magnetization in unison and langevin equations for a large spin

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Abstract

A single-domain ferromagnetic particle is represented as a large spin (model of rotation in unison) whose stochastic dynamics is derived from a spin-boson Hamiltonian. It is shown in the Markovian limit that thermal equilibrium exists provided that the fluctuation-dissipation theorem is supplemented by a symmetry constraint which for bilinear anisotropic and nonlinear (magnetoelastic) spin-bath coupling can only be satisfied in the underdamped limit. Only for bilinear isotropic coupling (Gilbert's theory) is it satisfied identically for arbitrary damping strength. Uniaxial and cubic symmetries are considered. For a model uniaxial crystal the thermal decay rate of M and the thermal enhancement of the macroscopic quantum tunneling rate are calculated for Gilbert and magnetoelastic dissipative couplings and compared. The effects of memory are discussed.

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Authors and Affiliations

  1. Department of Physics, National Taiwan University, Taipei, Taiwan 10764 R.O.C.

    Ivo Klik

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  1. Ivo Klik
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Klik, I. Rotation of magnetization in unison and langevin equations for a large spin. J Stat Phys 66, 635–645 (1992). https://doi.org/10.1007/BF01060085

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  • DOI: https://doi.org/10.1007/BF01060085

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