Ferroelectric-ferromagnetic correlations in BiMnO3 perovskite within Landau theory: comparison with experiment

Abstract

We discuss a simple phenomenological Landau theory of phase transitions with two coupled single-component order parameters and compare the results with available experimental data.The model corresponds to the case of a ferroic system, in which ferromagnetic and ferroelectric transitions originally occur at temperatures T M and T f , respectively. For T f > T M the magnetoelectric coupling strongly renormalizes the magnetic transition temperature, T M → T RM (with T RM >> T M ), as well as generates an additional anomaly in ferroelectric subsystem T RM . Full susceptibility tensor has also been determined. The concept of Arrot plot is replaced by the Arrot planes which appear when both types of order coexist. The results are in good overall agreement with experimental data for the ferroelectromagnetic BiMnO 3 . We also estimate the contribution of Gaussian fluctuations of both order parameters, that lead to corrections to the mean-field specific heat. Those corrections are still insufficient even though other quantities agree quite well with experiment. We calculate the temperature dependence of the coherence length for both types of order as well.

Proximate transition temperatures amplify linear magnetoelectric coupling in strain-disordered multiferroicBiMnO3

“…A previous treatment of BMO using Landau theory incorporates quartic, P 4 and M 4 , and biquadratic, (P M ) 2 , terms in the free energy [41]. In contrast, our finding in the above analysis that the angle-averaged free energy is minimum at θ 0 = 3π/2 implies that the conventional biquadratic coupling term ( P · M ) 2 in Eq.…”