Hybrid Improper Ferroelectricity: A Mechanism for Controllable Magnetization-Polarization Coupling

TL;DR

This paper demonstrates how hybrid improper ferroelectricity in layered perovskites enables control over magnetization and polarization through coupled structural and magnetic domains driven by oxygen octahedron rotations.

Contribution

It introduces the concept of hybrid improper ferroelectricity, showing how non-polar modes induce ferroelectricity and magnetoelectric effects in layered perovskites.

Findings

Oxygen octahedron rotations induce ferroelectricity and magnetoelectricity.

Hybrid improper ferroelectricity involves a combination of two non-polar modes.

Control over magnetism is achieved via octahedron rotation distortions.

Abstract

First-principles calculations are presented for the layered perovskite Ca$_3$Mn$_2$O$_7$. The results reveal a rich set of coupled structural, magnetic and polar domains in which oxygen octahedron rotations induce ferroelectricity, magnetoelectricity and weak-ferromagnetism. The key point is that the rotation distortion is a combination of two non-polar modes with different symmetries. We use the term "hybrid" improper ferroelectricity to describe this phenomenon and discuss how control over magnetism is achieved through these functional antiferrodistortive octahedron rotations.