Impurity spin in normal stochastic field: basic model of magnetic resonance

Famous Anderson-Weiss-Kubo model of magnetic resonance is reconsidered in order to bridge existing gaps in its applications for solutions of fundamental problems of spin dynamics and theory of master equations. The model considers the local field fluctuations as one-dimensional normal random process. We refined the conditions of applicability of perturbation theory to calculate the spin depolarization. It is shown that for very slow fluctuations the behavior of the longitudinal magnetization is simply related to the correlation function of the local field. The effect could be checked by the experimental studies of magnetic resonance in quasi-Ising paramagnets