Fluctuation effects on the magnetization dynamics below the Curie temperature of ferro- and ferrimagnets

摘要

Measurements of the linear dynamic susceptibility between 1 Hz and 20 GHz are reported for strongly uniaxial and weakly anisotropic cubic model magnets. Approaching T/sub c/ from below, the contributions of the homogeneous magnetization and the wall motion have been separated. The most significant effects of critical magnetization fluctuations occur in the wall mobility of uniaxial materials near the disordering temperature of the Bloch-walls, T*>T/sub c/ and in the stability region of linear walls, T*>T>T/sub c/. Moderate effects appear in the oscillator-like dynamics of the homogeneous magnetization in the cubic ferromagnets due to the crossover from exchange- to dipolar-dominated fluctuations, whereas the fluctuationless micromagnetic model based on |M/spl I.oarr/|=M/sub s/(T) and constant transverse relaxation parameter explains the Bloch-wall dynamics for T/spl les/0.9 T/sub c/ and H/spl les/0.4N M/sub s/.