Displacive magnetic phase transitions upon spin ordering in magnets with strong single-ion anisotropy

This paper reports on the results of investigations into the magnetic ordering of magnets with integer spins of ions and sufficiently strong easy-plane single-ion anisotropy. It is demonstrated that magnetic ordering in the studied systems occurs through a displacive magnetic phase transition. The magnetic polarization of ionic states, which spontaneously arises at the phase transition point, acts as an order parameter in displacive magnetic phase transitions. The magnetically ordered state in the magnets under consideration is formed as a result of competition between the exchange interaction and single-ion anisotropy.