Atomistic-model study of temperature-dependent domain walls in the neodymium permanent magnet Nd2Fe14B

We studied the properties of domain walls (DWs) of the Neodymium magnet, Nd2Fe14B. Applying an atomistic model, in which the magnetic moments of all atoms and exchange interactions were determined by a first-principles calculation (Korringa-Kohn-Rostoker Green's function method), we performed a Monte Carlo simulation for two types of DW, i.e., moving along the a axis and along the c axis, which are classified into a Bloch-type wall and a Neel-type wall, respectively. We found that the shapes of the DWs of both types are described well by those derived from the continuum model used in micromagnetics. We show that the estimated DW widths are very close to the experimentally evaluated ones. Furthermore, we discovered that the width of the latter type is smaller than that of the former type. We also investigated the temperature dependence of the DW width and found that at higher temperatures it becomes larger and the magnitude of the magnetization becomes smaller, which agrees with experimental observations.