Influence of microstructural change of the interface between Nd ₂Fe₁₄B and Nd-O phases on coercivity of Nd-Fe-B films by oxidation and subsequent low-temperature annealing

This study provides the influence of microstructural change of the interface between Nd₂Fe₁₄B and Nd-O phases on coercivity of Nd-Fe-B thin films during annealing at low temperature (∼350 °C). All films were prepared by using ultra high vacuum (UHV) magnetron sputtering, and the Nd-Fe-B layer was oxidized under Ar gas atmosphere (O₂ content; ∼2 Vol.ppm). Then, the films were annealed at 250-350 °C under UHV condition. After oxidation, the coercivity of Nd-Fe-B film decreased to around 40% of the coercivity of as-deposited Nd-Fe-B film. The Nd-rich phase changed from α-Nd to amorphous Nd(-O), and the interface of Nd₂Fe ₁₄B/Nd(-O) became rough. In the Nd-Fe-B films oxidized and subsequent annealed at 350 °C, the coercivity decreased to around 20%. In the films, poly crystalline hcp Nd₂O₃ phase crystallized in Nd-rich phase, and there were some steps at the surface of Nd₂Fe ₁₄B phase contacting with hcp Nd₂O₃ phase. Regardless of crystal orientation of Nd₂Fe₁₄B, the microstructural changes of the interface described above were observed.