Orientational memory site in hydrogenation disproportionation desorption recombination process of anisotropic Nd2Fe14B-based magnets

Abstract

To clarify the orientational memory site in the hydrogen disproportionation desorption recombination process of Nd2Fe14B-based anisotropic magnets, high resolution transmission electron microscopy (HRTEM) characterization of hydrogen disproportionated structure of Nd13.0Fe67.9Co11.0Ga1.0Zr0.1B7.0 has been performed. In particular, crystallographic orientations of disproportionated products relative to that of parent or original Nd2Fe14B have been carefully analyzed using partially disproportionated samples. No apparent orientational coherency exists between the disproportionated products of α-Fe, Fe2B, and NdH2 and the parent Nd2Fe14B. However, nanoscale Nd2Fe14B particles of 10 to 100 nm in diameter have been detected by HRTEM to be densely present within the disproportionated mixture. Lattice fringe observation has also revealed that the crystallographic axes of the Nd2Fe14B particles are nearly parallel to those of the original Nd2Fe14B. It is thus suggested that these Nd2Fe14B particles be the orientational memory site upon the recombination, which recovers the original orientation leading to the anisotropy formation.