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 degrees C followed by the postannealing at 550 degrees 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.