Effect of Nonmagnetic Cap Layers for Nd–Fe–B Thin Films With Small Addition of Rare-Earth Element

We have investigated the effect of nonmagnetic cap layers for Nd-Fe-B thin films with a small addition of rare-earth element. Remarkable enhancement of the coercivity was obtained for the Nd-Fe-B thin film on the epitaxially grown Mo buffer layer deposited at 500 °C followed by the postannealing at 550 °C. Especially, the highest room temperature (RT) coercivity H_C of 31.5 kOe can be obtained for the Nd-Fe-B (16 nm)/Nd-Cu (0.75 nm)/Al (0.6 nm) thin film. This result suggests that a eutectic reaction among Nd, Cu, and Al elements was occurred during the postannealing, and then the grain boundary between Nd₂Fe₁₄B main phases is refined by the diffusion of the cap layer. We demonstrated that the Nd-Fe-B thin film showed large H_c exceeding 30 kOe at RT without using heavy rare-earth elements.