The Study On Coupling Mechanism And The Magnetoelectric Properties In The Ferroelectromagnetic System

The ferroelectromagnets, in which ferroelectric ordering and magnetic spin ordering coexist spontaneously at low temperature, have been the object of intensive theoretical and experimental studies from the 60-70's last century for its connection with the finding out this kind of material and theirs some special properties of physics own to magnetoelectric coupling. By magnetoelectric coupling, the application of an electric field or ferroelectric polarization can change one or more of the parameters governing the magnetic behavior of the system. Correspondingly, being possible magnetostrictive effect or electron-phonon interaction, the fluctuation of spin ordering may lead to a dielectric anomaly and ferroelectric relaxation. So we can preview these new characters of this type of material on the aspect of physics property with study the magnetoelectric coupling between the ferroelectric ordering and magnetic ordering, ie, dielectric (magnetic) properties of the ferroelectromagnets may be altered by the onset of the magnetic (electric) trasistion or by the application of a magnetic (electric) field.There exists magnetoelectric effects in two type of material, one of them is spin-order material called magnetoelectrics that may exhibits an induced linear magnetoelectric effect by external field. This effect is named as the electrically induced magnetoelectric effect (ME) E or magnetically induced magnetoelectric effect (ME) H- A ferroelectromagnet, however, differs from the magnetoelectrics in that it shows spontaneous magnetoelectric effects in addition to the (ME) E, H effects induced by external fields. They are caused by the coexistence in the crystal of spontaneous ferroelectric and magnetic moments. An anomalies in the dielectric constants and loss tangent have been observed experimentally in the ferroelectromagnet near the antiferromagnetic transition temperature, indicative of a coupling between the ferroelectric and magnetic ordering, but the nature of the mechanism of magnetoelec coupling and the form of interaction is still an important and debated issue.In this paper, on the basis of a simple model, A-type antiferromagnet and Neel antiferromagnet, according to previous magnetoelectric theories, we analyze step by step the influence of electric field on spin spectrum, magnetoelectric coupling on the effect of external field, possible coupling form of magnetic and ferroelectric ordering in the case of perpendicular and parallel, and investigated magnetic, electric and magnetoelectric properties of cubic system in different coupling mechanism in the frame of spin-wave theory, mean-field approximation, and soft-mode theory. It is found that magnetoelectric coupling can result in the anomalies in the dielectric polarization in the low temperature, and the shift of the anomalies toward higher temperature. A weak ferromagnetic ordering is taken on the antiferromagnetic system with applying ferroelectric polarization or external electric field.