Study on magnetoelectric coupling in ferromagnetic/ferroelectric heterostructures

Abstract

Multiferroic materials have drawn increasing interest due to their abundant physics and potential for application. In multiferroic materials, the coupling interaction between the ferroelectric and ferromagnetic ordering could make new effect, called magnetoelectric (ME) effect. Magnetoelectric effect is defined as polarization P of a sample in an external magnetic field H (direct effect) or a variation of a sample magnetization M in an external electric field E (converse effect). There is lots of intensive study and widely investigated compound materials for searching proper ME materials. Despite of such constant efforts, their ME coupling is usually weak and only exist far below room temperature. It hinders their promising application On the other hand, strain-mediated indirect magnetoelectric coupling through combination of separately well defined ferromagnetic and ferroelectric material is considered. It called ME composites, which is made by combination of piezoelectric and ferromagnetic materials. This scenario may be realized via strain-induced spin reorientation transitions (SRTs) in FM layers.Especially, thin film ME heterostructures could permit precise magnetielectric study, because layer thickness and interfacial roughness may be controlled accurately. And also ferroelectric layers like PZT and PMN-PT can generate strains up to 1%. The ME effect in composite materials can be understood by the interplay between the inverse piezoelectric effect of the FE layer and the inverse magnetostrictive effect of the FM layer. That is, for the ME (CME) effect, when a magnetic field (electric field) is applied to a composite, the ferromagnetic phase(the piezoelectric phase) change its shape magnetostictively(piezoelectrictively). The stain is then passed along to the piezoelectric phase(ferromagnetic phase), resulting in an electric polarization(change of magnetizartion). Thus, the ME (CME) effect in composite is extrinsic, depending in the composite microstructur...