FLUCTUATION EFFECTS ON THE MAGNETIZATION DYNAMICS BELOW AND CURIE-TEMPERATURE OF FERROMAGNETS AND FERRIMAGNETS

Measurements of the linear dynamic susceptibility between 1 Hz and 20 GHz are reported for strongly uniaxial and weakly anisotropic cubic mo del magnets. Approaching T(c) from below the contributions of the homo geneous magnetization and the wall motion have been separated. The mos t significant effects of critical magnetization fluctuations occur in the wall mobility of uniaxial materials near the disordering temperatu re of the Bloch-walls, T < T(c) and in the stability region of linear walls, T < T < T(c). Moderate effects appear in the oscillator-like dynamics of the homogeneous magnetization in the cubic ferromagnets du e to the crossover from exchange- to dipolar-dominated fluctuations, w hereas the fluctuationless micromagnetic model based on \M\ = M(s) (T) and constant transverse relaxation parameter explains the Bloch-wall dynamics for T less-than-or-equal-to 0.9 T(c) and H less-than-or-equal -to 0.4 N M(s).