The Role of DFT Approach in Calculations of Magnetocrystalline Anisotropy in α″–Fe₁₆N₂

The ordered iron nitride phase α″–Fe₁₆N₂ is one of most promising candidates for rare earth–free magnets; validation of its magnetic anisotropy is critical to further improve its performance. So far, both experimental measurements (K_u ~ 4.4 × 10⁶ – 1.9 × 10⁷ erg/cc) and computational results (5.0 × 10⁶ – 1.6 × 10⁷ erg/cc) vary; the latter in particular depend strongly on the density-functional theory (DFT) approaches used. To address this issue, the plane-wave DFT code Quantum ESPRESSO was employed to more comprehensively study the effect of different DFT approaches on the system and its magnetocrystalline anisotropy (MCA) energy, particularly the influence of exchange-correlation (XC) functionals (from LDA through GGA+U) and pseudopotential methods, obtaining a range of results K_u ~ 4.0 × 10⁶ – 2.86 × 10⁷ erg/cc. The role and limitations of these approaches are discussed in light of band structure and density-of-state calculations. In addition, further research into the choice of Hubbard U,J parameters and other XC functionals, as well as alloying for increased anisotropy, are planned.

Cf.:
P. Stoeckl, P.W. Swatek, & J.P. Wang, AIP Advances: MMM (under review) & ref. cit.