Influence of Nd Oxide Phase on the Coercivity of Nd-Fe-B Thin Films

To understand the coercivity mechanism of Nd Fe B sintered magnets the microstructure of grain boundary composed of Nd2Fe14B and Nd rich phases has been studied However the influence of Nd rich phase which contains some amount of oxygen on microstructure and coercivity has not been clear In this study the influence and the interfacial microstructure between the Nd2Fe14B phase and the Nd rich phase were investigated using Nd Fe B thin films Furthermore the microstructural change of Nd oxide (Nd 0) phase was investigated using oxidized Nd thin films The coercivity (H-cJ) of the Nd Fe B thin films decreased by about 80% from the level of as deposited film (H-cJ(as depo)) after oxidation and annealing at low temperature (similar to 350 degrees C) From TEM observation of the Nd Fe B film some steps along the surface of the Nd2Fe14B phase contacting with the hcp Nd2O3 phase were observed Investigation of the microstructural change of Nd oxide phase was carried out using Nd thin films The as deposited Nd film was composed of the dhcp Nd (alpha Nd) phase and the fcc NdOx phase formed at the surface of a Nd phase after oxidation After annealing at 350 degrees C the hcp Nd2O3 phase crystallized from the fcc NdOx phase and it resulted in large roughness at the boundary with the alpha Nd phase From the results described above the crystallization of hcp Nd2O3 phase causes damage at the surface of Nd2Fe14B phase during the annealing at low temperature which results in the decrease of coercivity [doi 10 2320/matertrans MAW201019]