High pressure high-temperature behavior and magnetic properties of Fe4N: experiment and theory

Under high pressure high-temperature conditions, namely 8.5(8)GPa and 1373(150)K, -Fe4N (Pm3m) is transformed into E-type Fe3N0.75. At ambient temperature, the onset of the transition is observed above 17GPa by in situ X-ray diffraction data. The nitrogen content of Fe3N0.77(4) deduced on the basis of the observed lattice parameters is in excellent agreement with the result from chemical analysis (Fe3N0.760(6)O0.018(2)). The thermochemical properties of the product combined with calculations of the formation enthalpy indicate that, at ambient pressure conditions, E-Fe3N0.75 transforms back into N around 525K. Magnetization data of E-Fe3N0.75 show that the bulk sample is a soft ferromagnetic material. Ab initio methods yield a magnetization of 6.2 (B) for both E-Fe3N0.75 and the daltonide E-Fe3N but the local moments differ.