Transmission Electron Microscopy Study on Nd-Rich Phase at the Surface of ${\hbox {Nd}}_{2}{\hbox {Fe}}_{14}{\hbox {B}}$ Phase in Nd-Fe-B Films

This study provides the abundance ratio of Nd(-O) phases at the interface of Nd₂Fe₁₄B/Nd(-O) in Nd-Fe-B films with different coercivity values. The crystal structure and morphology of the Nd₂Fe₁₄B/Nd (-O) interface were investigated by transmission electron microscopy. In the Nd-Fe-B film annealed at 350°C, the coercivity of which decreases to around 20% of the value of as-deposited film, the hcp Nd₂O₃ phase are existed dominantly at the surface of Nd₂Fe₁₄B phase with c-plane and non-c-plane. (In this study, the planes of Nd₂Fe₁₄B with the c-axis perpendicular or non-perpendicular to the interface are described as “c-plane” and “non-c-plane”, respectively.) On the contrary, C-Nd₂O₃ and amorphous phases, which were metastable phases, existed dominantly in the film after annealing at 650°C, the coercivity of which recovers to the same level of as-deposited film. The abundance ratio of the metastable phases tends to be higher at the surface of non-c-plane than at the surface of c-plane of Nd₂Fe₁₄B phase.