Shapovalov I. Ordered phases and phase transitions in uniaxial SU(3)-magnets.

Model of a uniaxial magnet with unity spin in presence of single-ion anisotropy and anisotropic biquadratic exchange interaction in the most common form was studied. In this type of magnets quadrupole and quadrupole-ferromagnetic phase besides ordinary ferromagnetic phase can occur. The spectrum of spin excitations at finite temperatures in the ferromagnetic and two quadrupole phases was determined. The first order phase transition on the field between the ferromagnetic and the plane-quadrupole phase is accompanied by the hysteresis phenomena. An analytical expression for the remagnetization energy per single ion is obtained. An explicit analytical expression for the temperature of destabilization of spin excitation spectrum in absence of an external magnetic field was obtained.