Stability, elastic and magnetostrictive properties of γ-Fe4C and its derivatives from first principles theory

Using the first-principles full-potential linearized augmented plane-wave method, we investigated the stability, elastic and magnetostrictive properties of γ-Fe4C and its derivatives. From the formation energy, we show that the most preferable configuration for MFe3C (M=Pd, Pt, Rh, Ir) is that the M atom occupies the corner 1a position rather than 3c position. These derivatives are ductile due to high B/G values except for IrFe3C. The calculated tetragonal magnetostrictive coefficient λ001 value for γ-Fe4C is −380 ppm, which is larger than the value of Fe83Ga17 (+207 ppm). Due to the strong SOC coupling strength constant (ξ) of Pt, the calculated λ001 of PtFe3C is −691 ppm, which is increased by 80% compared to that of γ-Fe4C. We demonstrate the origin of giant magnetostriction coefficient in terms of electronic structures and their responses to the tetragonal lattice distortion.