Enhanced magnetic properties in chemically inhomogeneous Nd-Dy-Fe-B sintered magnets by multi-main-phase process

Homogeneous substitution of Dy for Nd in the hard magnetic 2:14:1 phase can effectively enhance coercivity to ensure the high temperature operation, however, inevitably deteriorate remanence at expense. In this work, we performed a comparative investigation of the two magnets prepared by multi-main-phase (co-sintering Nd₂Fe₁₄B and (Nd, Dy)₂Fe₁₄B powders) and single-main-phase (sintering (Nd, Dy)₂Fe₁₄B powders) approaches. The comparative investigation reveals that at the same Dy substitution level (2.16 wt%), such chemically inhomogeneous multi-main-phase magnet possesses better room-temperature magnetic properties as well as thermal stability than those of the single-main-phase one with homogenous Dy distribution in the matrix grains. Room-temperature magnetic properties H_cj = 1664 kA/m, B_r = 1.33 T and (BH)_max = 350.4 kJ/m³ for the multi-main-phase magnet are all better than those for the single-main-phase magnet with H_cj = 1536 kA/m, B_r = 1.29 T and (BH)_max = 318.4 kJ/m³. In addition, over the temperature range from 295 to 423 K, both the temperature coefficients of coercivity and remanence for the multi-main-phase magnet are also lower than that for the single-main-phase magnet. Such superior magnetic performance is attributed to the short-range magnetic interactions inside individual 2:14:1 phase grains and the long-range magnetostatic interactions between adjacent grains with inhomogeneous Dy distribution. Our work provides a feasible approach of enhancing coercivity and retaining energy product simultaneously in the Nd-Dy-Fe-B permanent magnets.