Pressure-induced successive magnetic and structural phase transitions in Fe1.087Te

The crystal and magnetic structures of Fe1.087Te have been studied by neutron powder diffraction in the temperature range from 5 to 170 K at pressures in the range from approximate to 0.8 to approximate to 7 GPa. The p, T-phase diagram contains three phases with monoclinic, orthorhombic and tetragonal symmetry. The monoclinic and orthorhombic phases are both antiferromagnetically ordered and stable at temperatures below approximate to 69 K while the non-magnetic tetragonal phase is stable above this temperature. The monoclinic phase is stable for p less than or similar to 1.2 GPa while the orthorhombic phase is stable for 1.2 less than or similar to p less than or similar to 1.7 GPa and the tetragonal phase becomes stable at higher pressures at the lowest measured temperatures. The magnetic ordering is antiferromagnetic bicollinear and commensurate in the monoclinic phase but incommensurate and pressure dependent in the orthorhombic phase. The pressure-induced collapse of magnetic order at approximate to 1.7 GPa is accompanied by abrupt changes in volume and compressibility, suggestive of a spin state change of the Fe2+ ions in the FeTe layers.