Theoretical analysis of Cu addition effects in Nd-Fe-B magnets

To understand the mechanism, we simulated Cu-doped Nd2Fe14B/NdOx systems, which werediscovered around triple junctions in annealed Nd-Fe-B magnets and Cu is thought tosurround the main phases. We used the computational code OpenMX within density functionaltheory. In our model structures Cu is around the interface between the main phase(Nd2Fe14B) and the subphase (NdOx). After simulated various model structures, we comparedtheir total energies to check where Cu prefers to be in the model structures. We found thatthe model structures which Cu located at the interstitial space between the main phase andthe subphase, and the Fe site at the interface in the main phase are the most stable. Inaddition, we discovered that the anisotropy of Nd and Fe atoms at the interface is essentiallynegative. By considering the total energy and anisotropy analyses, we concluded thatsubstituting the Fe site with Cu at the main-phase interface can be one possivle scenario ofexplaining the coercivity improvement in Cu-doped Nd-Fe-B magnets since its coercivity isimproved by 40 % compared to that of the non-Cu-doped Nd-Fe-B system.