Abstract
The effect of pressure on the magnetic and electronic properties of synthetic FeS and Fe7S8 has been investigated by using 57Fe Mössbauer and electrical resistance measurements on polycrystalline samples pressurized in miniature gem anvil cells up to a pressure of ∼12 GPa in the temperature range 300–5 K. FeS in the low-pressure phases (P ≲ 7 GPa) has thermally activated charge carriers and a high-spin electronic configuration along the room temperature isotherm, whereas the high-pressure monoclinic phase (P ≳ 7 GPa) adopts a magnetically quenched low-spin state and a non-metallic behaviour associated with the filled valence band. The non-metallic behaviour observed in all pressure phases is explained in terms of electron correlation between Fe:3d electrons. In contrast, Fe7S8 is magnetic-metallic below ∼5 GPa and diamagnetic-metallic above this pressure. The metallic behaviour is ascribed to hole conduction in the S:3p band, as inferred from the temperature dependence of the Mössbauer data. The collapse of band magnetism at ∼5 GPa in Fe7S8 may be due to pressure-induced band broadening, leading to a breakdown of the Stoner criterion.
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