Ferroelectric-ferromagnetic correlations in BiMnO 3 perovskite within Landau theory: comparison with experiment

Here we present a simple model formulated in the spirit of Landau theory in order to qualitatively describe magnetoelectric multiferroics. The system consists of two coupled single-component order parameters P and M which represent ferroelectric and ferromagnetic phases, respectively. We show that the magnetoelectric coupling strongly renormalizes the original magnetic transition temperature, T M $\rightarrow$ T RM (with T RM ≫ T M ), as well as generates an additional anomaly in ferroelectric subsystem at T RM . Under the influence of both magnetic and electric fields the concept of Arrot plot is reproduced by the Arrot planes. We compare obtained results with available experimental data for the BiMnO 3 which undergoes ferroelectric transition below 700 K (T f ) and ferromagnetic transition at 100 K (T RM ). 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. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010