First-principles study of intersite magnetic couplings in NdFe_(12) and NdFe_(12)X (X = B, C, N, O, F)

摘要

We present a first-principles investigation of NdFe_(12) and NdFe_(12)X (X = B, C, N, O, and F) crystals with the ThMn_(12) structure. Intersite magnetic couplings in these compounds, the so-called exchange couplings, are estimated by using Liechtenstein's method. It is found that the Nd-Fe couplings are sensitive to the interstitial dopant X, with the Nd-Fe(8j) coupling in particular reduced significantly for X = N. This suggests that magnetocrystalline anisotropy decays quickly with rising temperature in the X = N system although nitrogenation has advantages over other dopants in terms of enhancing low-temperature magnetic properties. The Curie temperature is also calculated from the magnetic couplings by using the mean field approximation. Introduction of X enhances the Curie temperature, with both structural changes and chemical effects found to play important roles in this enhancement.