Microstructure optimization to achieve high coercivity in anisotropic Nd–Fe–B thin films

Abstract A high coercivity of 2.35 MA m−1 (29.5 kOe) is demonstrated using perpendicular anisotropy Nd–Fe–B films. Single layer columnar grown Nd–Fe–B thin films with a coercivity comparable with that of sintered magnets (1.11 MA m−1, 14.0 kOe) were used as the starting film. The coercivity was doubled by annealing films capped with Nd, Nd/Cu, and Nd/Ag layers. Transmission electron microscopy indicated that the Nd2Fe14B columnar grains were isolated by a Nd-rich grain boundary phase formed by diffusion of the capped layers into the grain boundaries of the polycrystalline Nd–Fe–B films. The temperature dependence of coercivity was lower than that of commercial sintered magnets. The coercivity of the Nd/Cu diffusion processed sample at 473 K was 0.979 MA m−1 (12.3 kOe), which is higher than that of Nd10Dy4Fe80B6 sintered magnets.