Magnetoelectric effects on ferromagnetic and ferroelectric phase transitions in multiferroic materials

The magnetoelectric effects on ferromagnetic and ferroelectric phase transitions in multiferroic materials were researched experimentally and theoretically. Shifts of the ferroelectric/ferromagnetic Curie temperature under magnetic/electric fields were observed due to the magnetoelectric coupling in magnetoelectric composites. We employed the Landau method with a Gibbs free energy function including ferroelectric, ferromagnetic and magnetoelectric items to understand our experimental results and some recent reports. The numerical simulations presented some important conclusions, including the jump of magnetization/polarization near the ferroelectric/ferromagnetic phase transition, the shifts of Curie temperature under external fields and the enhancement of magnetoelectric susceptibility near the Curie temperatures. These calculations coincide very closely with the experimental results. The magnetoelectric limitation (χme2<χm·χp) was also proved with this simple method. The results indicate that parameters such as Curie temperature, polarization, magnetization and susceptibilities can be adjusted by the magnetic or electric field.