The hexagonal Fe₂P (h-Fe₂P, space group: P-62m) is a well-known binary phase and it has been considered as the only stable Fe₂P structure at ambient pressure. Its orthorhombic polymorph (o-Fe₂P, space group: Pnma) was first reported in 1976 as a high-pressure phase but did not receive much attention until geologists found the same structure polymorph of iron meteorite, allabogdanite, (Ni,Fe)₂P. It was later found that allabogdanite and o-Fe₂P can be made under ambient pressure but there was no report about how to grow the single crystal of pure o-Fe₂P and synthesize the single phase of the bulk powder. In this study, we synthesized single phase of o-Fe₂P bulk powder using Sn flux method, indicating o-Fe₂P is another stable polymorph at ambient conditions. In situ powder X-ray diffraction and differential scanning calorimetry studies showed that the formation of o-Fe₂P phase is a thermodynamically favorable process and the phase transition from o-Fe₂P to h-Fe₂P happens as low as 550 °C, indicating o-Fe₂P is a low temperature polymorph. Magnetic property measurement showed that both polymorphs are ferromagnetic. The o-Fe₂P phase exhibited lower saturation magnetization than h-Fe₂P but had a higher ordering temperature. The partial substitution of Fe with other 3d transition metals using the same synthesis method still preserved the orthorhombic structure and their different magnetic properties would be presented.

Seongyoung Kong

Appearances