Dramatic volume collapses under pressure are fundamental to geochemistry and of increasing importance to fields as diverse as hydrogen storage and high-temperature superconductivity. In transition metal materials, collapses are usually driven by so-called spin-state transitions, the interplay between the single-ion crystal field and the size of the magnetic moment. Here we show that the classical S=5/2 mineral Hauerite undergoes an unprecedented 22 % collapse driven by a conceptually different magnetic mechanism. Using synchrotron x-ray diffraction we show that cold compression induces the formation of a disordered intermediate. However, using an evolutionary algorithm we predict a new structure with edge-sharing chains. This is confirmed as the thermodynamic groundstate using in situ laser heating. We show that magnetism is globally absent in the new phase, as low-spin quantum S=1/2 moments are quenched by dimerisation. Our results show how the emergence of metal-metal bonding can stabilise giant spin-lattice coupling in Earth's minerals.
@article{arxiv.1305.7119,
title = {Giant pressure-induced volume collapse in the pyrite mineral MnS2},
author = {Simon A. J. Kimber and Ashkan Salamat and Shaun R. Evans and Harald O. Jeschke and Kaliappan Muthukumar and Milan Tomic and Francesc Salvat-Pujol and Roser Valenti and Maria V. Kaisheva and Ivo Zizak and Tapan Chatterji},
journal= {arXiv preprint arXiv:1305.7119},
year = {2014}
}