QUANTITATIVE CHARACTERIZATION OF ADDITIONAL FERROMAGNETIC PHASE IN MELT-QUENCHED AND SINTERED ND-FE-B-BASED MAGNETS

Quantitative evidence of a ferromagnetic Fe-rich minor phase present i n both melt-quenched/die-upset and sintered magnets based on the Nd2Fe 14B composition is presented. Full hysteresis loops were obtained at e levated temperatures (650 K less than or equal to T less than or equal to 800 K) and were subsequently decomposed to obtain the saturation m agnetization M(s) of the minor phase as well as the paramagnetic slope of the 2-14-1 major phase as a function of temperature. Assuming a co mposition of pure iron, the calculated volume % of the impurity phase in the die-upset magnets is consistent with that obtained from previou s observations of the widths and geometry of the intergranular phase f ound in the same magnets. The magnetization of the ferromagnetic impur ity phase in the melt-quenched magnets decreases more rapidly than tha t of pure iron; extrapolation indicates a Curie temperature in the ran ge 925 K<T<975 K. The paramagnetic susceptibility of the Nd2Fe14B main phases exhibits Curie-Weiss behavior with the same paramagnetic Curie temperature for both sintered and die-upset samples. The Curie consta nts differ, however, probably due to the different degrees of crystall ographic alignment. (C) 1996 American Institute of Physics.