Efficient co-diffusion of Tb and Co in a sintered Nd-Fe-B magnet by low-melting point alloys

Co-diffusion of heavy rare-earth elements and Co has been reported to improve the remanence and coercivity of Nd-Fe-B magnet at high temperatures without trade-off. Two low-melting point alloys Pr50Tb20Cu15Co15 and Y15Pr40Tb15Cu15Co15 were designed in this work to simultaneously enhance the remanence and coercivity at 150 & DEG;C in sintered magnet by grain boundary diffusion. The remanence increased from 1.24 T to 1.28 and 1.31 T at 150 & DEG;C together with the increase of coercivity from 0.3 T to 0.89 and 0.77 T after diffusion. The temperature coefficients of remanence (20-150 & DEG;C) were reduced from -0.11 %/& DEG;C to -0.07 and -0.06 %/& DEG;C by Pr50Tb20Cu15Co15 and Y15Pr40Tb15Cu15Co15 respectively. The improvement of temperature coefficients is attributed to the microstructure effect without changing the Curie temperature. The low melting point of the diffusion alloys and Y are attributed to breaking the remanence-coercivity dilemma with reduced Tb and Co usage.