First-Principles Study of Magnetocrystalline Anisotropy and Magnetization in NdFe12, NdFe11Ti, and NdFe11TiN

We study magnetic properties of NdFe12, NdFe11Ti, and NdFe11TiN theoretically from first-principles. These materials are related to strong ferromagnets containing rare-earth elements. The crystal electric field parameter A(20) at the Nd site is calculated using the density functional theory in the generalized gradient approximation, with the open-core treatment for the Nd-f states. A(20) in NdFe12 is 1 83 K, while substitution of an iron atom at the 8i site with titanium changes the sign of A(20), suggesting that the Ti substitution induces a complex magnetic structure. Interstitial nitrogenation substantially increases A(20) to 439 K, which is consistent with strong uniaxial anisotropy observed in the experiments. Titanium substitution suppresses the magnetization substantially, whereas nitrogenation enhances the magnetization.