Coupling-induced ferromagnetic transitions in ferroelectromagnets of weak antiferromagnetic order

A Monte-Carlo simulation on phase transitions in ferroelectromagnets (FEMs) in which a weak antiferromagnetic ordering occurs at the Neel point TN far below the ferroelectric ordering point TE was performed. It is revealed that an intrinsic coupling between spins and electric-dipoles (mp-coupling) does result in a weak ferromagnetic transition from the paramagnetic state at a temperature far above TN, as long as the coupling is strong enough. The magnetoelectric properties as a function of temperature, mp-coupling strength and external electric and magnetic fields were investigated. A mean-field calculation based on the Heisenberg model was performed and a rough consistency between the simulated and calculated ferromagnetic transitions was shown.