Coherent ensemble of pseudospins in an external field

The behavior in time is considered for the state vector of an ensemble of coherent pseudospins in external permanent and variable fields. Relaxation of the state vector of the ensemble is described by a Landau-Lifshits equation. The vector equation of motion is reduced to a first-order differential equation. Exact solutions of this equation are obtained for different combinations of both weak and strong fields acting on the ensemble. Conditions for applicability of the solutions obtained are discussed.