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

## TL;DR

This paper develops a theoretical framework to understand how electric polarization can emerge at surfaces of magnetic materials, thin films, and multilayers, highlighting two distinct mechanisms involving surface-induced interactions.

## Contribution

It introduces a theoretical model distinguishing two pathways for surface-induced multiferroicity based on the presence of Dzyaloshinskii-Moriya interactions in magnetic materials.

## Key findings

- Surface-induced electric polarization can occur via two different mechanisms.
- The presence or absence of Dzyaloshinskii-Moriya interactions determines the multiferroic behavior.
- Experimental implications of the theory are discussed.

## 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 developed theory.