Nano-Dimensional analysis of high-performance Nd-Fe-B-Based magnetic materials for micro-structural control

Changes in microstructure of Nd-Fe-B based magnetic materials were investigated with advanced electron microscopes to study the Tb diffusion treatment for high coercivity for sintered magnets and the hydrogenation- decomposition-desorption- recombination (HDDR) process for high anistropic magnet powders. In sintered magnets, it was found that morphology of a Nd- rich wetting-layer phase changes to be continuous in shape and uniform in thickness in association with diffusion of Tb. The formation of the continuous Nd-rich wetting-layer phase containing a small amount of Tb leads to an effective increase in coercivity. In the HDDR magnet powder, a recombined Nd ₂Fe ₁₄B phase is formed first as a rim phase on spherical NdH ₂ grains during the DR-process. Small grain size of NdH ₂ phase and large grain size of a-Fe matrix after the HD-process can produce small grains of highly aligned Nd ₂Fe ₁₄B that lead to high remanence and high coercivity. These results indicate that a nano-dimensional analysis is essentially important to develop the high-performance of magnetic materials.