Magnetic Properties of Substituted R₂(Fe, Al, Co)₁₄B Compounds


The effects of the substitution of Fe by Al in R2(Fe1-xAlx)14B compounds (R = Y, rare earths) on their magnetic properties have been investigated. The compounds crystallize in the tetragonal structure, P42/mnm, provided x < 0.01. The saturation magnetization and Curie temperatures decrease slightly with increasing Al content, x. However, the anisotropy constant, K1, and the anisotropy field, HA, exhibit a maximum at x = 0.06. The substitution of Fe with Al atoms is also effective in enhancing the coercivity of magnets based on the Nd-Fe-B compounds. As the Y atom carries no magnetic moment, the increased anisotropy field must result from preferential ordering of nonmagnetic Al atoms among the six nonequivalent crystallographic sites of the iron sublattice. Earlier work has shown that the replacement of Fe by Co results in increasing the Curie temperature and decreasing the coercive field. The present data show that the Nd-(Fe, Al, Co)-B magnets have both high Curie temperatures and high coercive forces. Accordingly, it appears that it is possible to improve the thermal properties and reduce the total losses of Nd-Fe-B magnets by appropriate substitution of Fe with Al and Co atoms.



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