Low Temperature Physics: 32, 768 (2006); https://doi.org/10.1063/1.2219498 (11 pages)
Fizika Nizkikh Temperatur: Volume 32, Number 8-9 (August 2006), p. 1010-1023    ( to contents , go back )

Spin wave damping under spin orientation phase transitions

V.G. Baryakhtar and A.G. Danilevich

Institute of Magnetism of the National Academy of Sciences of Ukraine 36-b Vernadsky Ave. Kiev 03142, Ukraine
E-mail: bar@imag.kiev.ua

Received February 6, 2006, revised March 21

Abstract

The spin wave spectra and damping in the vicinity of spin orientation phase transitions were investigated. It is shown that the Landau– Lifshits relaxation term cannot describe the spin wave damping in the case of degenerate basic state with a continuous degeneracy parameter. A dissipative function for ferromagnetic crystals of different symmetry was constructed. The cases of finite and zero longitudinal magnetic susceptibility were considered. Method of calculating the relaxation term in the Landau— Lifshits equation for crystals of different symmetry was given. The spin wave spectra and damping were calculated for ferromagnets with uniaxial and tetragonal symmetry. It is shown, that relaxation is a two-stage process. At the first stage of relaxation an equilibrium magnitude of magnetization intensity is established due to the exchange interaction. At the second stage of relaxation there occurs a damping of the spin wave amplitude as the magnetization variable precesses round its equilibrium value. The detailed elaboration of N.N. Bogolubov method of quasi-middle is debated with reference to ferromagnets with spontaneously degenerated vacuum.

PACS:
76.20.+q - General theory of resonances and relaxations
75.25.+z - Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.) (for devices exploiting spin polarized transport, see 85.75.-d)

Key words: ferromagnetic, phase transition, spin wave damping, dissipative function, dispersion law.

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