Magnetic phase transition of FeS at high pressures

Abstract

RMC simulation of the experimental structure factor was successfully applied to generate a reliable 3-dimensional atomic configuration. Several partial atomic pair correlation functions, like the g SiO (r), g BO (r), g OO (r), g SiSi (r), g SiB (r), g NaO (r), g BaO (r), g ZrO (r) According to the cosmochemical arguments and the seismological data, the Earth's core must contain some light elements. However, the nature of the light element is still uncertain, and the major proposed candidates have been C, Si, O, H, or S. Therefore, it is important to understand the phase relationships of iron alloys at high pressures and high temperatures. In this study, we conducted high-pressure experiments and ab inito calculations to investigate the phase transitions and the physical properties of iron sulfide. In the case of highpressure experiments, the laser-heated diamond anvil cell combined with the synchrotron X-ray diffraction technique was used [1]. We also used the first-principle calculations to investigate the magnetic property of highpressure phase, which was discovered in the high-pressure experiments [2]. According to previous studies at ambient temperatures, FeS exhibits the following sequence of highpressure phase transitions: troilite (FeS-I), low-P MnP phase (FeS-II), monoclinic phase (FeS-III). In our highpressure experiments, we confirmed that the monoclinic phase was stable up to 40 GPa. Above 40 GPa, the sample was heated to 1000-2000 K to induce the phase transition. After heating, a new high-pressure phase (high-P MnP phase) was observed. This high-P MnP phase (FeS-VI) remained stable at pressures higher than 120 GPa. We found a significant discrepancy between low-P MnP and high-P MnP phases. The discontinuities for the unit cell volume and the cell parameters between two phases were observed. As the structure of low-P MnP phase is identical to that of high-P MnP phase, these discontinuities indicated that an unknown type of phase transition must occur. Next, we investigated the magnetic properties and the spin configurations of these phases using the ab inito calculations. Previous study [3] confirmed that the low-P MnP phase was antiferromagnetic state. The same results were confirmed in our calculations. We also calculated the non-magnetic state for the MnP structure. The calculated results showed that the non-magnetic MnP structure was more stable than anti-ferromagnetic MnP structure at high pressures. The volume and cell parameters of nonmagnetic MnP structure were in good agreement with those of high-P MnP phase observed in our experiments. Therefore, the magnetic transition of the MnP structure occurred at high pressures. The high-pressure stability limit of the high-P MnP phase was also investigated. We found that the phase transition from the high-P MnP phase to the CsCl-type phase occurs at about 300 GPa. Thus, the high-P MnP phase is stable at pressures corresponding to the lower mantle and the outer core. In contrast, the CsCltype phase is stable in the inner core. Our new findings can c...

Nano-Sized Iron Sulfide: Structure, Synthesis, Properties, and Biomedical Applications

“…FeS can also be used as a superconductor (Kwon et al, 2011 ). Even when the structure of FeS is changed from troilite to the MnP-type under high pressure, the antiferromagnetic properties are preserved until the monoclinic structure is formed (Ono, 2007 ). The magnetic moment then disappears and yetragonal-phase FeS (Tc: 5K) was observed for the same structure as the superconductor FeSe (Tc: 8 K) (Kuhn et al, 2016 ).…”