Variable pressure-temperature neutron diffraction of wüstite (Fe1−xO): Absence of long-range magnetic order to 20GPa

Abstract

Neutron diffraction measurements have been performed on polycrystalline Fe1−xO (wüstite) up to 20.3GPa using a large-volume moissanite anvil cell at room temperature to examine the existence of long-range magnetic ordering in the high-pressure rhombohedral phase of the material. This investigation is crucial for understanding the nature of high-pressure phase transitions in Fe1−xO. Low temperature ambient pressure neutron diffraction measurements on the same sample were also conducted at 190, 180, and 85K to compare with the high-pressure results. Magnetic peaks are expected to be observed under pressure similar to those at 180K at ambient pressure. However, no magnetic peaks were evident in the high-pressure diffraction patterns (to 20.3GPa at 300K). The absence of magnetic peaks indicates the absence of long-range magnetic order in Fe1−xO under these conditions. This result indicates the need to reconsider the interpretation of high-pressure Mössbauer studies and the mechanism of the high-pressure phase transitions in Fe1−xO.