Theoretical study of static and dynamic properties of orthorhombic multiferroic substances

The influence of the magnetoelectric coupling and the exchange interaction constants on different magnetic and dielectric properties of orthorhombic RMnO, multiferroic materials is studied based on the transverse ising and Heisenberg models using a Green's function technique. In the vicinity of the phase transition temperature T, we obtain an anomaly, a kink in the temperature dependence of the magnetic properties. This is due to the coexistence of ferroelectricity and magnetism which leads to interplay between the electric and magnetic properties. The spin excitations show a novel softening around T, due to the magnetoelectric coupling. The effect of external electric and magnetic fields is also calculated. We obtain the magnetic-field-induced polarization and the electric-field-induced magnetization. The obtained results are in qualitative agreement with the experimental data. (c) 2008 WILEY-VCH Veriag GmbH & Co. KGaA, Weinheim.