First-principles study of the effect of Cu and NdOx in Nd2Fe14B magnets

Recent experimental studies tells us that understanding of interactions between grain boundaries and main phases in Nd-Fe-B magnets might be important in order to know the mechanism of its coercivity and magnetic anisotropy energy (MAE). Until now, improvement of coercivity has been reported because of the existence of Nd oxides (NdOx) with fcc Nd sublattice. Furthermore, the coercivity of Nd-Fe-B magnets are enhanced by the Nd-Cu grain boundary diffusion process. From this study, Cu is supposed to be around the main phases. To clarify the mechanism of the enhancement of the coercivity of Nd-Fe-B magnets, Nd2-yCuyFe14B/NdOx system is a suitable system for the first step calculation by the density functional theory. We calculate this system using the computational code OpenMX. First, we calculated Nd1.75Cu0.25Fe14B where one Nd site is substituted for Cu, and found that substituting Nd for Cu at the 4g site is more stable than at the 4f site from the comparison of total energies of these two phases. We determined the metastable structure of NdOx as Nd4O (x = 0.25) with the zinc blend structure.