Theory of surface-induced multiferroicity in magnetic materials, thin films, and multilayers

Abstract

We present a theoretical study of the onset of electric polarization close to a surface in magnetic materials and in thin films and multilayers. We consider two different paths that lead to the onset of multiferroic behavior at the boundary in materials that are bulk collinear ferromagnets or antiferromagnets. These two paths are distinguished by the presence or absence of a surface induced Dzyaloshinskii-Moriya interaction which can be taken into account through Lifshitz invariants in the free energy of the system. Experimental consequences are discussed in the light of the theory.

Room-temperature surface multiferroicity in Y$_2$NiMnO$_6$ nanorods

“…They were shown to result from extended spin-orbit coupling in lower dimension [14]. In a recent theoretical work [15], it has been claimed that a bulk and collinear ferro-or antiferromagnet supports surface ferroelectricity both in presence and absence of surface induced Dzyaloshinskii-Moriya (DM) exchange interaction. These new developments are, therefore, precipitating a new paradigm of surface/interface multiferroicity which is distinct even from multiferroicity in the composite systems where striction mediated coupling between magnetic and ferroelectric order parameters across the interfaces of constituent phases is the key feature.…”