Effect of Hubbard U on calculations of magnetic properties of α″–Fe16N2

Abstract

The ordered iron nitride phase α″–Fe16N2 has been a potential candidate for rare-earth free magnets with giant saturation magnetization, but first-principles electronic-structure calculations have struggled to reproduce recent observations of high magnetic moment, while calculations of magnetocrystalline anisotropy (MCA) vary significantly. Within the framework of density-functional theory (DFT), a common extension to the usual generalized-gradient approximation (GGA) exchange-correlation (XC) functional is the inclusion of Hubbard parameters U (,J) as GGA + U. A number of previous papers have applied this method to Fe16N2, each with their own choice of Hubbard parameters. The plane-wave DFT code Quantum ESPRESSO was employed to more comprehensively study the effect of the value of Hubbard parameters U and J on the system, particularly with respect to its magnetic properties. Various approaches for setting U and J were compared, including self-consistent calculations via the linear-response method.