Nd-Fe-B/Nd(-O) interfaces were prepared by thin film technique for the investigation of relationship between interfacial state and coercivity. A Nd-Fe-B layer was deposited by UHV magnetron sputtering and the film was oxidized under low vacuum conditions. On the oxidized Nd-Fe-B layer, a Nd layer was deposited and the film was annealed at 250650°C. The coercivity of Nd-Fe-B layer decreased after the oxidation. However, it recovered after the deposition of Nd layer and the annealing at 350°C. High-resolution transmission electron microscopy (HRTEM) observations revealed that an fcc NdO phase forms after the oxidation and an amorphous phase exists along the interface between Nd2Fe14B and Nd2O3 phases after annealing at 350°C. Therefore, the recovery of coercivity is related to the amorphous phase, which is considered to be formed by the transformation from NdO to Nd2O3 and α-Nd, and the release of strain at the interface.

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