Kuznetsov A. Relaxation of elementary excitation in the nematic phase of non-Heisenbergs magnets with spin S=1

Thesis for candidate's degree by speciality 01.04.11 - magnetism. - V. I.Vernadskiy Tavrida National University, Simferopol 2011. In this work with the mechanism of generalized coherent states of group SU(3) magnons relaxation processes were studied in nematic state of magnets with spin S = 1. General presentation of isotropic exchange interaction was considered. For three dimensional spin nematic over the entire range of its existence, including SU(3) transition point to ferromagnetic state, magnon excitations appear slightly damping and have Goldstone behavior. In particular, in case of wave vector close to zero, decrement of damping matches to zero rather than frequency excitations. Taking into account single-ion anisotropy of type "easy axis" for the spins leads to the fact that anisotropic nematic state with anisotropy of type "easy plane" for vector-director appears. For anisotropic spin nematic there are two branches of magnons. Magnons without activation are slightly damping but magnon decrement is proportional to fourth power of wave frequency for three dimensional model in case of long-wave approximation. This outstanding behavior due to influence of other branch of magnon spectra. Damping of activation magnons due to interraction with non-activation magnons and it is proportional to the power of temperature for all range of temperatures.