Quantitative characterization of additional ferromagnetic phase in melt-quenched and sintered Nd endash Fe endash B-based magnets

Quantitative evidence of a ferromagnetic Fe-rich minor phase present in both melt-quenched/die-upset and sintered magnets based on the Nd2Fe14B composition is presented. Full hysteresis loops were obtained at elevated temperatures (650 K≤T≤800 K) and were subsequently decomposed to obtain the saturation magnetization Ms of the minor phase as well as the paramagnetic slope of the 2-14-1 major phase as a function of temperature. Assuming a composition of pure iron, the calculated volume % of the impurity phase in the die-upset magnets is consistent with that obtained from previous observations of the widths and geometry of the intergranular phase found in the same magnets. The magnetization of the ferromagnetic impurity phase in the melt-quenched magnets decreases more rapidly than that of pure iron; extrapolation indicates a Curie temperature in the range 925 K≤T≤975 K. The paramagnetic susceptibility of the Nd2Fe14B main phases exhibits Curie endash Weiss behavior with the same paramagnetic Curie temperature for both sintered and die-upset samples. The Curie constants differ, however, probably due to the different degrees of crystallographic alignment. copyright 1996 American Institute of Physics