Multiferroicity and skyrmions carrying electric polarization in GaV4S8

TL;DR

This paper investigates the multiferroic properties of GaV4S8, revealing its complex magnetic phases including skyrmion lattices, and demonstrates the potential for electric field manipulation of skyrmions due to its strong magnetoelectric coupling.

Contribution

It uncovers the coexistence of ferroelectricity and multiple magnetic phases in GaV4S8, and predicts spatial modulation of polarization near skyrmions, advancing skyrmion control methods.

Findings

GaV4S8 exhibits a sizable ferroelectric polarization of ~1 μC/cm2.

Multiple multiferroic phases coexist, including skyrmion lattice with modulated polarization.

Exchange striction is identified as the key mechanism behind spin-driven ferroelectricity.

Abstract

Skyrmions are whirl like topological spin objects with high potential for future magnetic data storage. It is a fundamental question, relevant for both basic research and application, if a ferroelectric (FE) polarization can be associated with their magnetic texture and if these objects can be manipulated by electric fields. Here, we study the interplay between magnetism and electric polarization in the lacunar spinel GaV4S8, which undergoes a structural transition associated with orbital ordering at 44 K and reveals a complex magnetic phase diagram below 13 K, including a ferromagnetic (FM), cycloidal, and N\'eel-type skyrmion lattice (SkL) phase. We found that the orbitally ordered phase of GaV4S8 is FE with a sizable polarization of ~1 {\mu}C/cm2. Moreover, we observed spin-driven excess polarizations in all magnetic phases and, hence, GaV4S8 hosts three different multiferroic phases with coexisting polar and magnetic order. These include the SkL phase where we predict a strong spatial modulation of the FE polarization close to the skyrmion cores. By taking into account the crystal symmetry and spin patterns of the magnetically ordered phases, we identify the exchange striction as the main microscopic mechanism behind the spin-driven FE polarization in each multiferroic phase. Since GaV4S8 is unique among the known SkL host materials due to its polar crystal structure and the observed strong magnetoelectric effect, this study is an important step towards the non-dissipative electric-field control of skyrmions.