Electron theory of interstitial dopant dependence of magnetic properties in NdFe11TiX (X= B, C, N, O, F)

Currently the strongest permanent magnet compound is Nd₂Fe₁₄B. At room temperature, its magnetization is 1.60 T and magnetocrystalline anisotropy field is 67 kOe [1]. There are many works to find a material which has better intrinsic magnetic properties than those of Nd₂Fe₁₄B. NdFe₁₁TiN is a good candidate of the permanent magnet. It has comparably large magnetocrystalline anisotropy 80 kOe [2] or more than 70 kOe [3] at room temperature. However, its magnetization 1.48 T [3] is smaller than that of Nd₂Fe₁₄B. In NdFe₁₁TiN, Ti works for stabilization of the system but it significantly reduces the magnetic moment [4]. Recently NdFe₁₂N has been synthesized as a film and shown to have better magnetic properties [5]. Its magnetization and magnetocrystalline anisotropy at room temperature are 1.66 T and 80 kOe, respectively. For NdFe₁₁TiN and NdFe₁₂N, nitrogen atom at interstitial site has an important role for the enhancement of magnetization and magne-tocrystalline anisotropy. The interstitial doping can be an important method for development of permanent magnet materials.