ON THE NONLINEAR DYNAMICS AND RELAXATION OF STRONGLY ANISOTROPIC FERROMAGNETS

It is shown that in a strongly anisotropic S=1 ferromagnet the equations for four parameters describing the spin dynamics may be reduced to two Lorentz-invariant equations for the spin components in the easy plane of a ferromagnet. Such simplification is possible for the case of the weak easy plane anisotropy and near the transition into the quadruple phase. In the case the macroscopic long-wave description of magnetic solitons is adequate. Solitons of two types existing in such magnets are studied. Only one type of solitons proves to be stable. The relaxation processes' in this system are analyzed. In the whole range of parameters, with the exception of the narrow vicinity of the transition point into quadruple state, magnons are strongly damping. The braking of domain wall-like solitons is also larger than in weakly anisotropic magnets.