Giant pressure-induced volume collapse in the pyrite mineral MnS₂

Orateur : Dr. Simon A. J. KIMBER (European Synchrotron Radiation Facility ESRF – Grenoble )

Minerals which contain magnetic metals may collapse under the pressures found in the Earth’s mantle. These so-called spin-state transitions are due to the reduction of the magnetic moment associated with each metal atom. Here we report the discovery of a giant volume collapse in the mineral Hauerite (MnS₂) under pressure. Instead of a change in the single-ion magnetic moments, this is driven by the Mn²⁺ cations spontaneously forming pairs, or dimers. In contrast to the magnetic, unpaired electrons found at ambient pressure, the dense new phase thus contains an ordered arrangement of chemical bonds which are globally non-magnetic. This ’squeezing out’ of magnetism is shown to stabilize the huge increase in density.

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