Transformation of coercivity mechanism and evolution of microstructure in high performance Nd-Dy-Fe-Co-B thick films

Abstract

It is important to understand the relationship between coercivity and microstructure for the development of high performance rare-earth permanent magnets. In this paper, the effects of film thickness on perpendicular magnetic anisotropy, coercivity mechanism, magnetization reversal process and microstructure of Nd-Dy-Fe-Co-B thick films are systematically investigated by varying film thickness from 1 to 12 µm. It is found that the coercivity mechanism transforms from a mixed type dominated by pinning to another mixed type dominated by nucleation. In addition, the evolution of grain shape from irregular spherical crystals to columnar ones occur at film thickness of 3 µm. The columnar crystals form on the capping layer and grow toward the buffer layer. When the film is thicker than 6 µm, Nd elements accumulate on the Ta buffer layer. With increasing the film thickness, the columnar crystal structure can grow throughout the whole thick film, and the Nd-rich phase is extruded onto the buffer layer, while the pinning effect weakens and the nucleation mechanism is dominated. This work can help us better understand the relationship between coercivity mechanism and microstructure of thick rare-earth permanent magnetic films.