On the multiferroic skyrmion-host GaV4S8

TL;DR

GaV4S8 is a multiferroic material hosting Nel-type skyrmions, exhibiting complex magnetic phases, ferroelectric polarization, and a transition from antiferromagnetic to ferromagnetic exchange interactions, with detailed experimental insights into its properties.

Contribution

This study provides comprehensive experimental characterization of GaV4S8, revealing its multiferroic nature, complex magnetic phases, and the molecular-like behavior of V4 clusters, expanding understanding of skyrmion-host materials.

Findings

GaV4S8 exhibits skyrmion-lattice phases with multiferroic properties.

The magnetic exchange interaction switches from antiferromagnetic to ferromagnetic at the Jahn-Teller transition.

V4 clusters behave as molecular units with spin 1/2, with fluctuating moments at high temperatures.

Abstract

The lacunar spinel GaV4S8 exhibits orbital ordering at 44 K and shows a complex magnetic phase diagram below 12.7 K, which includes ferromagnetic and cycloidal spin order. At low but finite external magnetic fields, N\'eel-type skyrmions are formed in this material. Skyrmions are whirl-like spin vortices that have received great theoretical interest because of their non-trivial spin topology and that are also considered as basic entities for new data-storage technologies. Interestingly, we found that the orbitally ordered phase shows sizable ferroelectric polarization and that excess spin-driven polarizations appear in all magnetic phases, including the skyrmion-lattice phase. Hence, GaV4S8 shows simultaneous magnetic and polar order and belongs to the class of multiferroics, materials that attracted enormous attention in recent years. Here, we summarize the existing experimental information on the magnetic, electronic, and dielectric properties of GaV4S8. By performing detailed magnetic susceptibility, resistivity, specific heat, and dielectric experiments, we complement the low-temperature phase diagram. Specifically, we show that the low-temperature and low-field ground state of GaV4S8 seems to have a more complex spin configuration than purely collinear ferromagnetic spin order. In addition, at the structural Jahn-Teller transition the magnetic exchange interaction changes from antiferromagnetic to ferromagnetic. We also provide experimental evidence that the vanadium V4 clusters in GaV4S8 can be regarded as molecular units with spin 1/2. However, at high temperatures deviations in the susceptibility show up, indicating that either the magnetic moments of the vanadium atoms fluctuate independently or excited states of the V4 molecule become relevant.