Effect of pressure on the structural, magnetic, dynamical and mechanical properties of α″-Fe16N2

The ground-state properties of the α″-Fe₁₆N₂ compound have been thoroughly studied, while its physical properties under high pressure are unknown. Here, the effect of pressure on the structural, electronic, magnetic, mechanical and dynamical properties of the α″-Fe₁₆N₂ are systematically investigated from the first principles calculations. The theoretical results at 0 GPa are consistent with previous theoretical and experimental values. The critical pressure of ferromagnetic collapse (P_C) is about 61.2 GPa. The magnetic moments of the Fe atoms at 4d and 4e sites are the largest and smallest, respectively. The Fe moments are mainly derived from the spin polarization of the d_z² and d_x²_-y² electrons. From the phonon spectra, the α″-Fe₁₆N₂ exhibits the dynamic stability below the P_C, and the Fe atoms at the three sites show different vibrational anisotropy under high pressure. According to the B/G and Poisson’s ratios, the Fe₁₆N₂ exhibits excellent metallic ductility below the P_C. The elastic modulus increases with pressure, but softens near the critical pressure. In addition, the elastic anisotropy also mutates near the critical pressure P_C.