Effect of the magnetoelectric exchange interaction on temperature-related phase transitions in a ferroelectric antiferromagnetic material
Abstract
It is shown that the magnetoelectric exchange interaction in a ferroelectric antiferromagnetic material with the Curie point below the Néel point gives rise to new temperature-related first- and second-order phase transitions. In the spin subsystem, moreover, it becomes possible that the magnetic sublattices will flop upon a change of temperature. The magnetoelectric interaction induces a temperature-related metamagnetic transition. The ferroelectric transition changes from second-order to first-order at magnetic field intensities near the spin-flop level, and in a strong magnetic field the Curie temperature shifts by an amount proportional to the magnetic field intensity squared. A tetracritical point, a critical point of second-order transitions, and several triple-phase points appear on the phase diagram of equilibrium states in the (H,T)-plane.