Coercivity evolution and suppressed thermally activated defects in diffusion processed Nd-Fe-B films

The single-layer Ta(20 nm)Nd₁₃Fe₇₇B₁₀(100 nm)Ta(20 nm)film was prepared and diffusion-processed by Nd₂₅Cu₇₅(20 nm)and Nd₇₀Cu₃₀(20 nm). The evolutions of microstructure and magnetic properties were comparably studied. By using same amount of diffusion layer, different coercivities were achieved. The coercivity enhancement mechanism was explained phenomenologically by surface defects of Nd₂Fe₁₄B grains and estimation of activation volume. It was found that due to the increased Nd composition in grain boundaries, the activation volume was reduced and the local anisotropy was enhanced due to the remedied surface defect. Such dependence was consistent with the coercivity changes.