BACKWARD HELICAL WAVES IN SPATIALLY DISORDERED MAGNETIC MEDIA

A nonlinear evolution system of hydrodynamic-type equations describing a three-dimensional multisublattice magnet is studied. An explicit ex pression is obtained for the energy density function of magnetic syste ms whose energy density is invariant to right-and left-spin rotations. Exact solutions for spin density are obtained in the form of helical waves for quadratic-biquadratic dependence of the energy density (in t erms of Cartan's invariant functions) in three-dimensional case. Solut ions are also obtained for magnon fields inducing such waves. The exis tence of backward helical waves is predicted. (C) 1998 American Instit ute of Physics.