Low Temperature Crystal Structures and Magnetic Properties of the V4-Cluster Compounds Ga1-xGexV4S8

TL;DR

This study investigates the structural and magnetic evolution of the solid solution Ga1-xGexV4S8, revealing how substituting Ga with Ge influences crystal symmetry, magnetic ordering, and phase transitions across the composition range.

Contribution

It provides detailed insights into the structural phase transitions and magnetic properties of Ga1-xGexV4S8, highlighting the effects of electron count variation on magnetic ordering and symmetry changes.

Findings

Magnetic moments increase linearly with Ge content.

Transition from ferromagnetic to antiferromagnetic order around x <= 0.5.

Structural phase transitions occur across the composition range, with rhombohedral and orthorhombic distortions.

Abstract

The solid solution Ga1-xGexV4S8 (x = 0 - 1) was synthesized by solid state reactions and characterized by temperature-dependent x-ray powder diffraction and static magnetic susceptibility measurements. The compounds crystallize in the cubic GaMo4S8-type structure (space group F-43m), built up by heterocubane-like [V4S4](5-x)+ cubes and [Ga1-xGexS4](5-x)- tetrahedra arranged in a NaCl-like manner. The successive substitution of Ga3+ by Ge4+ increases the electron count in the molecular orbital (MO) of the V4-cluster gradually from seven to eight. We observe an almost linear increase of the magnetic moments, connected with a transition from ferromagnetic to antiferromagnetic ordering around x <= 0.5. Remarkably, the low temperature structural phase transitions as known from the ternary compounds were also detected in the solid solution. The gallium-rich compounds (0 < x < 0.5) undergo rhombohedral distortions like GaV4S8 (space group R3m), whereas distortions to orthorhombic symmetry (space group Imm2) as known from GeV4S8 occur in the germanium-rich part of the solid solution (0.5 <= x < 1).