Contributions of magnetic structure and nitrogen to perpendicular magnetocrystalline anisotropy in antiperovskite ε-Mn4N

To study how nitrogen contributes to perpendicular magnetocrystalline anisotropy (PMA) in the ferrimagnetic antiperovskite Mn4N, we examined both the fabrication of epitaxial Mn4N films with various nitrogen contents and first-principles density-functional calculations. Saturation magnetization (M-s) peaks of 110 mT and uniaxial PMA energy densities (K-u) of 0.1 MJ/m(3) were obtained for a N-2 gas flow ratio (Q) of similar to 10% during sputtering deposition, suggesting nearly single-phase crystalline epsilon-Mn4N. Segregation of alpha-Mn and nitrogen-deficient Mn 4 N grains were observed for Q approximate to 6%, and were responsible for a decrease in the M-s and K-u. The first-principles calculations revealed that the magnetic structure of Mn 4 N showing PMA was "type B," having a collinear structure, whose magnetic moments couple parallel within the c plane and alternating along the c direction. In addition, the K-u calculated using Mn32Nx supercells showed a strong dependence on nitrogen deficiency, in qualitative agreement with the experimental results. The second-order perturbation analysis of K-u with respect to the spin-orbit interaction revealed that not only spin-conserving but also spin-flip processes contribute significantly to the PMA in Mn4N. We also found that both contributions decreased with increasing nitrogen deficiency, resulting in the reduction of K-u. It was noted that the decrease in the spin-flip contribution occurred at the Mn atoms in face-centered sites. This is one of the specific PMA characteristics we found for antiperovskite-type Mn4N.