Magnetodielectric effects in the ferroelectric ferromagnet BiMnO₃

Abstract

The changes in the dielectric constant of perovskite BiMnO 3 at about T C , 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 perovskitetype ferroelectromagnet BiMnO 3 , 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 χ p around T C , and the field-induced change in the magnetocapacitance effect becomes maximal at T C , which are in good agreement with experimental data in ferroelectromagnetic BiMnO 3 .

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

“…χ e (T ) exhibits a trend observed experimentally with increasing H a , but the calculated changes are too large. However, the corresponding temperature range is reproduced to much better accuracy than that of [20], where the calculated temperature T RM is far too low. The magnetic-susceptibility data follow roughly the Curie-Weiss law with the paramagnetic Curie temperature Θ M ≈ 120K.…”

“…(19)(20) it directly effects the rapid increase of electric polarization and magnetization in ordered state and is the greatest possible value for the coupling.…”

“…In some papers [16,20] this is rationalized on the basis of Landau-theory yet this it is not the case. In fact, in this phenomenological approach the inverse susceptibility is a linear function of the squared magnetization and it comes about from the renormalization of dielectric constant by the coupling.…”

Specific features of magnetic structure formation in orbitally degenerate BiMnO3 manganite

“…The orbital structure will be described using a model of electron vibrational (vibronic) interactions as described by the following Hamiltonian [12,13]: (2) Let us consider partial contributions stipulated by this model. The main linear contribution from the near est neighbor oxygen environment of manganese ion can be written as and V e = -1.29 eV/Å is the linear vibronic interaction constant determined in [14].…”

“…Bismuth manganite BiMnO 3 has been treated in many investigations as a multiferroelectric compound [1][2][3][4][5][6]. However, the results of recent experiments [7,8] have shown that this ferromagnetic crystal belongs to the C2/c symmetry group, which excludes the exist ence of spontaneous polarization [5][6][7][8][9].…”