First-principles study of intersite magnetic couplings in NdFe12 and NdFe12X (X = B, C, N, O, F)

We present a first-principles investigation of NdFe12 and NdFe12X (X = B, C, N, O, and F) crystals with the ThMn12 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.