Isotropic non-Heisenberg magnet with two sublattices (1, 1/2): Statics and dynamics

•Studied the influence of non-Heisenberg exchange interaction on the phase states of isotropic ferrimagnet.•Shown that the quadrupolar-ferrimagnetic phase can realize in the system.•Found the line of magnetic moments compensation for the quadrupolar-ferrimagnetic phase.•The phase transition from the quadrupolar-ferrimagnetic phase is of the second order. In the mean-field approximation, static and dynamic properties of isotropic ferrimagnet with two sub-lattices with spin equaling one and spin one-half are investigated. It was shown that the account of non-Heisenberg (biquadratic) exchange interaction can lead to the realization of the phase characterized with vector order parameters (ferrimagnetic phase) or of the phase, characterized by both vector and tensor order parameters (quadrupolar-ferrimagnetic)..The quadrupolar-ferrimagnetic phase realizes due to the account of biquadratic exchange interaction in the first spin-1 sub-lattice. The type of the phase transition and the conditions of the magnetic moments compensation were determined.