HIGH-PRESSURE COLLAPSE OF MAGNETISM IN FE0.94O - MOSSBAUER-SPECTROSCOPY BEYOND 100 GPA

First studies of Mossbauer spectroscopy to pressures above 100 GPa are reported. The magnetic state of Fe0.94O was investigated to 120 GPa a t T less than or equal to 300 K. At 300 K a diamagnetic low-spin (LS) state of Fe2+ is detected at 90 GPa: its abundance increases with P. T he gap between the T-5(2g) high-spin ground state and the (1)A(1g) LS excited state decreases with increasing P and at 120 GPa the LS specie s, first observed at 70 K, is fully converted at similar to 450 K. The magnetic collapse of Fe1-xO is an isochoric, second-order transition resulting front a gradual increase in the crystal-field with increasin g pressure.