Spin-driven symmetry breaking in the frustrated fcc magnet MnS2

TL;DR

This study reveals a new low-temperature phase in MnS2 caused by magnetic-lattice coupling, which reduces magnetic frustration and influences magnetic ordering, using high-resolution synchrotron X-ray diffraction.

Contribution

It reports the discovery of a symmetry-breaking phase transition in MnS2 driven by magnetic interactions, a novel insight into frustrated fcc magnets.

Findings

Detection of a pseudo-tetragonal distortion below 48 K

Refinement of structure in space group Pbca

Symmetry lowering reduces magnetic frustration

Abstract

We report the characterisation of natural samples of the cubic pyrite mineral MnS2 using very high resolution synchrotron X-ray diffraction techniques. At low temperatures we find a new low temperature polymorph, which results from coupling between magnetic and lattice degrees of freedom. Below the magnetic ordering temperature T_N= 48 K, we detect a pseudo-tetragonal distortion with a tiny c/a ratio of 1.0006. The structure can be refined in the space group Pbca. The symmetry lowering reduces magnetic frustration in the fcc Mn2+ lattice and is likely responsible for the previously reported lock-in of the magnetic propagation vector. This behaviour is similar to the frustration driven symmetry breaking reported in other three-dimensional Heisenberg magnets like the chromate spinels