Effect of Dy/Nd double layer on coercivity in Nd-Fe-B thin films

The Nd-Fe-B (t_NFB = 30 nm)/[Dy (t_Dy nm)/Nd (t _Nd nm)] (t_Dy/Nd = 20 nm) (thickness t_Dy = 0-10 nm) thin films were deposited on Al₂O₃(0001) substrate and subsequently in-situ annealed at 470 °C. As-deposited Nd-Fe-B thin films with a highly perpendicular orientation of c-axis were deposited by introducing bcc-Mo(111) single crystal buffer layer. After post-annealing, the grain size of the Nd-Fe-B/Dy/Nd thin films with the t_Dy = 10 nm and t_Nd = 10 nm becomes large due to the Dy and the Nd atoms thermal diffusion, while DyFe₂ and Dy oxide compounds are formed in Nd-Fe-B layers, which is confirmed by means of a combination of atomic force microscopy observation and X-ray diffraction measurement. The H_c of Nd-Fe-B/Dy/Nd thin films with the t_Dy = 10 nm and t_Nd = 10 nm was approximately the same value of the Nd-Fe-B thin films without Dy/Nd double layer annealed at 470 °C. On the other hand, H_c is enhanced to be about 22.1 kOe in the annealed Nd-Fe-B/Dy/Nd films with the t_Dy = 0.8 nm and t _Nd = 19.2 nm.