Low-frequency dynamics of many-sublattice magnet

A study is made of the low-frequency dynamics of a many-sublattice magnet with exchange interaction. On the basis of the Landau–Lifshitz equations with dissipative term, it is shown that at time $t\gg \tau _r$ ($\tau _r$ is the relaxation time) a reduced description of the state of the magnet arises. The complete system of dynamical equations of the many-sublattice magnet for the parameters of the reduced description, namely, the density of the total spin and the real rotation matrix, is determined.