Interfacial Microstructure of Nd2Fe14B/Nd-Rich and Coercivity in Nd-Fe-B Films

This study provides the relationship between phase change of Nd-rich and microstructural changes of Nd2Fe14B/Nd-rich interface in Nd-Fe-B films with different coercivity values. In as-deposited Nd-Fe-B film, flat interface of Nd2Fe14B/dhcp Nd is mainly observed. After oxidation, oxidized region was observed at the surface of Nd2Fe14B phase, and Nd2Fe14B/fcc NdOx interface were observed. In the Nd-Fe-B film subsequently annealed at 350 degrees C after oxidation, the coercivity of which decreases to around 20% of the value of as-deposited film, and the hcp Nd2O3 phase exists dominantly at the surface of Nd2Fe14B phase. In addition, there are some damaged regions at the surface of Nd2Fe14B phase. On the contrary, both the metastable C-Nd2O3 and amorphous phases existed dominantly at the Nd2Fe14B/Nd-rich interface of the film annealed at 650 degrees C. The coercivity of this film recovered to the same value of as-deposited film. These results indicate that the crystallization of hcp Nd2O3 phase include some damages to neighboring Nd2Fe14B phase decrease coercivity. During annealing at 550 to 650 degrees C, Nd-rich liquid phase appears and modifies the surface of Nd2Fe14B, and the coercivity recovers. After cooling, this liquid phase seems to crystallize into a C-Nd2O3 or an amorphous phases at the surface of Nd2Fe14B phase. In other words, the C-Nd2O3 or amorphous phases can exist without decreasing coercivity.