Structure and magnetic properties of NdFeB powder surrounded with layer of rare-earth fluorides

摘要

The effect of a layer of rare-earth fluorides on the structure and magnetic properties of NdFeB powders was studied. Rare-earth fluorides such as REF_x (RE: rare-earth element, x=2 or 3) were grown using fluoride liquid solutions in order to cover the surface of the NdFeB powders. For NdF_x-coated NdFeB powder, NdF_3 with a hexagonal structure was grown below 400 deg C. A structure change from NdF_3 to cubic NdF_2 was observed after annealing at the temperature of 400 deg C or more. Coercivity (_iH_c) for 3 vol percent NdF_x-coated NdFeB powder decreased to 14.0 from 15.0 kOe for noncoated NdFeB powder after annealing at 800 deg C. The rare-earth fluoride layers of LaF_x-, TbF_x-, and DyF_x-coated NdFeB powders showed a _iH_c of 16.8, 16.6, and 16.4 kOe, respectively, all of which were higher than that for noncoated NdFeB powder, indicating a diffusion of rare-earth atoms in the fluoride layer. .