Structure and magnetism of the skyrmion hosting family GaV$_4$S$_{8-y}$Se$_y$ with low levels of substitutions between $0 \leq y \leq 0.5$ and $7.5 \leq y\leq 8$

TL;DR

This study investigates how small levels of sulfur/selenium substitution in GaV$_4$S$_8$ and GaV$_4$Se$_8$ affect their structural and magnetic properties, revealing suppression of phase transition temperatures and the disappearance of skyrmion states at higher substitutions.

Contribution

It provides new insights into how minimal chemical substitutions influence the phase behavior and skyrmion stability in GaV$_4$S$_8$-type materials.

Findings

Substitutions suppress the structural phase transition temperature.

Skyrmion lattice states are present at very low substitution levels.

Higher substitution levels lead to disordered magnetic states.

Abstract

Polycrystalline members of the GaV$_4$S$_{8-y}$Se$_y$ family of materials with small levels of substitution between $0 \leq y \leq 0.5$ and $7.5 \leq y\leq 8$ have been synthesized in order to investigate their magnetic and structural properties. Substitutions to the skyrmion hosting parent compounds GaV$_4$S$_8$ and GaV$_4$Se$_8$, are found to suppress the temperature of the cubic to rhombohedral structural phase transition that occurs in both end compounds and to create a temperature region around the transition where there is a coexistence of these two phases. Similarly, the magnitude of the magnetization and temperature of the magnetic transition are both suppressed in all substituted compounds until a glassy-like magnetic state is realized. There is evidence from the $ac$ susceptibility data that skyrmion lattices with similar dynamics to those in GaV$_4$S$_8$ and GaV$_4$Se$_8$ are present in compounds with very low levels of substitution, $0 < y< 0.2$ and $7.8 < y < 8$, however, these states vanish at higher levels of substitution. The magnetic properties of these substituted materials are affected by the substitution altering exchange pathways and resulting in the creation of increasingly disordered magnetic states.