Ab-initio calculations of magnetic properties in Nd-Fe-B magnets with Cu existing around theinterface

To understand the mystery of the coercivity improvement in Cu-doped Nd-Fe-B magnets, westudied the magnetic properties of Cu-doped Nd2Fe14B/NdOx systems, which werediscovered around triple junctions in annealed Nd-Fe-B magnets. The crystal structure ofNdOx is known as the fluorite-type crystal structure determined by ab-initio studies andexperiments. We used the computational code OpenMX within density functional theory. Inorder to reduce computational costs as much as possible, we used an open-corepseudopotential of Nd atoms in which well-localized 4f electrons are treated as core electrons.By comparing formation energies of several model structures, we find that model systemswhere Cu is at the interstitial space or the Fe site in the main-phase interphase are morestable than a non-Cu-doped system. In addition, we analyzed the anisotropy of Nd and Fe inthe main phase and we can see that Nd and Fe atoms at the interface show negativeanisotropies. Furthermore, the anisotropy of Nd atoms which are next to a Fe-substituted sitewith Cu has been improved due to the weak magnetic coupling between Cu and Nd.