Magnetodielectric effects in the ferroelectric ferromagnet BiMnO3

The changes in the dielectric constant of perovskite BiMnO3 at about TC, which are induced by the magnetic ordering as well as by the application of magnetic fields, indicate that coupling exists between the magnetism and the dielectric properties. The soft-mode theory based on the single-well potential model and the molecular-field approximation to the Heisenberg model are successfully applied to the electric and magnetic subsystems coexisting in the perovskite-type ferroelectromagnet BiMnO3, respectively. By adding an appropriate coupling term, which is related to a combination of electrical polarization and spin correlation, we investigate the inherent coupling between the ferroelectric and ferromagnetic orders, and find that the application of magnetic fields induces a fairly large suppression of χp around TC, and the field-induced change in the magnetocapacitance effect becomes maximal at TC, which are in good agreement with experimental data in ferroelectromagnetic BiMnO3