Magnetic properties of rapidly crystallized Nd-Fe-B glassy alloys

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 a amorphous state by melt spinning, and then recrystallized at very high heating rates to control the microstructure. This process increased the intrinsic coercivity by about 30%. 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 ratio, Hci increases monotonically with Nd content 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. The temperature dependence of Hci is explained by the intrinsic temperature dependences of the magnetic anisotropy and local demagnetization field.