Composition and temperature dependence of coercivity of Nd-Fe-B alloys crystallized from the amorphous state (abstract)

Abstract

As a first step to study the role of second phases in achieving excellent hard magnetic properties in Nd-Fe-B permanent magnets we have prepared Nd-Fe-B alloys, near the Nd2Fe14B composition, with a maximum variation of 10 at. % Nd and 5 at. % B. The alloys were first quenched into an amorphous state by melt spinning, as previous studies on crystallization kinetics suggest better control on the microstructure and hence better hard magnetic properties of the recrystallized alloys. For all compositions with Nd concentrations 1 at. % greater than that of Nd2Fe14B the intrinsic coercivity Hci is above 1.2 T at 100 °C. For a constant Nd/B ration, Hci increases monotonously with Nd constant while for compositions where even small amounts of α. Fe form as a crystallization product Hci shows a sharp drop. On the other hand, it appears that B content is much less significant in determining Hci. The temperature dependence of Hci is almost linear for all compositions between 20 and 200 °C and is much better than that for sintered materials. Hci at room temperature of our samples is about 20% higher than that of commercial rapidly quenched materials with similar composition.