Magneto-orbital helices and multiferroicity

TL;DR

This paper reports the discovery of a magneto-orbital helix in CaMn7O12 that induces a record-high magnetically driven ferroelectric polarization, revealing new mechanisms for multiferroicity driven by orbital and structural order.

Contribution

It uncovers a novel magneto-orbital helix in CaMn7O12 that stabilizes a chiral magnetic structure and enables multiferroicity through structural and orbital coupling.

Findings

Largest magnetically induced ferroelectric polarization measured to date

Orbital order stabilizes chiral magnetic structures

Structural rotation couples polarization and magnetic helicity

Abstract

Orbitally ordered states evolving coincidentally with structural distortions and magnetic ordering provide a novel route to controlling electronic and magnetic properties of materials through external fields. We report an unprecedented magneto-orbital helix in CaMn7O12, found to give rise to the largest magnetically induced ferroelectric polarisation measured to date. Characterisation of the structural modulation using x-ray diffraction, and analysis of magnetic exchange shows that orbital order is crucial in stabilising a chiral magnetic structure, thus allowing for electric polarisation. Additionally, the presence of a global structural rotation enables the coupling between this polarisation and magnetic helicity required for multiferrocitiy. These novel principles open up the possibility of discovering new high-temperature multiferroics.