Magnetoelectric signature in the magnetic properties of antiferromagnetic multiferroics: Atomistic simulations and phenomenology

An effective Hamiltonian approach is used to reveal the effects of the (biquadratic) magnetoelectric (ME) coupling between local electric dipoles and local magnetic moments on magnetic properties of antiferromagnetic multiferroics. In addition to showing that the Neel magnetic ordering temperature (T-N) can strongly depend on such coupling, the simulations also reveal that the perpendicular component of the magnetic susceptibility, (XM,perpendicular to), can present some strong deviations from that of a typical antiferromagnet because of the ME coupling. Examples of systems for which T-N is lower than the first-order paraelectric-to-ferroelectric transition temperature (T-C) are (1) a discontinuity of (XM,perpendicular to) at T-C; (2) the inverse of the magnetic susceptibility not following anymore the traditional Curie law when the temperature ranges between T-N and T-C; and (3)(XM,perpendicular to) increasing with temperature, rather than forming a plateau, when the system is heated up to T-N. A Landau-type phenomenological model is further developed to reproduce and understand all these effects.