Effect of Cu addition on coercivity and interfacial state of Nd-Fe-B/Nd-rich thin films

This study provides the effect of Cu addition on coercivity (H _cJ) and interfacial microstructure in Nd-Fe-B/Nd-rich thin films. All films were deposited by using ultra high vacuum (UHV) magnetron sputtering, and the Nd-Fe-B layer was oxidized under several atmospheres with different oxygen content. Then, the films were annealed at 250-550 °C under UHV. The films oxidized in low vacuum (10^-2-10^-5 Pa) (under low oxygen state) exhibited the recovery of H_cJ by the annealing at 450 °C. On the contrary, the H_cJ of the films oxidized in Ar (under high oxygen state) decreased with increasing annealing temperature. However, the H_cJ increased drastically at the temperatures above 550 °C. In addition, the Cu added films, which were annealed at temperatures above 350 °C, showed higher coercivities than the films without Cu addition. The XRD analysis suggested the existence of C-Nd₂O₃ phase in the Cu added films annealed at 550 °C. It can be considered that the Cu addition decreases the eutectic temperature of Nd-rich phase and influences the interfacial state between Nd₂Fe₁₄B and Nd-rich phase.