Origin of the Verwey Transition in Magnetite

Comprehensive x-ray powder diffraction studies were carried out in magnetite in the 80–150 K and 0–12 GPa ranges with a membrane-driven diamond anvil cell and helium as a pressure medium. Careful data analyses have shown that a reversible, cubic to a distorted-cubic, structural transition takes place with increasing pressure, within the ($P,T$) regime below the Verwey temperature $T_V(P)$. The experimental documentation that $T_V(P)=T_{\mathrm{dist}}(P)$ implies that the pressure-temperature-driven metal-insulator Verwey transition is caused by a gap opening in the electronic band structure due to the crystal-structural transformation to a lower-symmetry phase. The distorted-cubic insulating phase comprises a relatively small pressure-temperature range of the stability field of the cubic metallic phase that extends to 25 GPa.