Microstructure of anisotropic Nd-Fe-B film magnets prepared by pulsed laser deposition

Microstructure of the anisotropic Nd-Fe-B thick-film magnets has been investigated by transmission electron microscopy. Specimens of the thick-film magnets were prepared by the high-speed pulsed laser deposition method with a substrate heating system. It was revealed that the film deposited on a Ta substrate has a three-layer structure of Nd2Fe14B: The lower layer is composed of isotropic grains about 50-300 nm in diameter, the middle one has a columnar structure of 1 mu m in height, and the upper one is again composed of small isotropic grains about several ten nm in diameter. The three-layer-structure is explained to result from a partial recrystallization of micro-crystal line Nd2Fe14B that are formed at the moment of deposition. In the middle layer, the c-axis of columnar grains is fairly aligned in the direction perpendicular to the substrate surface. The preferred orientation of c-axis produces the magnetic anisotropy of the thick-films.