Low field relaxation under dynamical perturbations

A zero (low) field resonance and relaxation theory is presented. It is applicable for the analysis of dynamical properties of μSR and NMR experiments. Interacting spin systems under a time-dependent random magnetic field are analyzed both for single crystals and powder samples. Besides orientational average over random configuration of molecules, a stochastic path averaging procedure is employed to obtain the time evolution of the probability density and averaged physical quantities.