MESOSCOPIC MODEL FOR THE PRIMARY RESPONSE OF MAGNETIC-MATERIALS (INVITED)

A model for the relaxation of thermal fluctuations is applied to the d ynamical response of magnetic materials. Systems investigated include paramagnets, spin glasses, and ferromagnets. The key feature which dis tinguishes the model is that it describes the behavior of localized no rmal modes (e.g., magnons), not barrier hopping or domain-wall motion. Mathematical approximations to the model reproduce several previously used empirical formulas, such as the stretched exponential, power-law , and logarithmic time dependences, but the unapproximated model gives generally better agreement with observed response. Data of sufficient quality and range allow quantitative confirmation of all assumptions of the model. The model provides a common physical basis for observed magnetic after-effects, the magnitude and distribution of Landau-Lifsh itz damping parameters, and 1/f noise.