TO THE THEORY OF HIGH-FREQUENCY PROPERTIE S OF FERROELECTROMAGNETIC MATERIAL WITH NONFROZEN ORBITAL MOMENT

The elementary excitations of an uniaxial ferroelectric-ferromagnetic material with a weak <<unfrozen>> orbital moment are studied. The magn etic subsystem is described by two moments, these being spin and orbit al magnetic moments of a ion connected by a spin-orbital interaction. The spectrum of magnetic and Ferroelectric excitations is studied in m agnetic fields parallel and perpendicular to the easy axis. It is show n that the distinct dependence of the spin and orbital magnetic moment s on a magnetic field perpendicular to spontaneous magnetization is re sponsible for a crossover of the spin and orbital branches and a split in the spectrum of ferromagnetic resonance. The contribution of the o rbital excitations to total magnetic moment is calculated. This contri bution has a temperature dependence different from that of the spin wa ves. The obtained results can be also applied to systems with two grou ps of magnetic ions. In this case the magnetic moment on one of the gr oups is of a spin nature, and in the other is of spin and orbital char acters. The weak interaction between the magnetic moments of the group s is of an exchange rather than a spin-orbital nature.