Effect of Co and Zr on magnetic properties of nanophase PrFeB alloys

Nanostructured ribbons in the compositional series Pr-12(Fe100-xCox)(82)B-6, x=0-30, having mean crystallite sizes d(g) in the range of 35-45 nm, were produced by overquenching and annealing. These had excellent second quadrant loop shapes and magnetic property combinations (H-i(c)=390-785 kA/m, (BH)(max)=100-220 kJ m(-3)), equivalent to those obtained previously by direct quenching to the nanocrystalline state. In particular, these excellent combinations of properties were obtained without additions of a grain refining agent, such as Zr, which has been reported to be a requirement for obtaining good loop shapes and properties for overquenched and annealed ternary melt spun PrFeB alloys. An additional advantage of the Co substitution for Fe is enhanced Curie temperature. It was found, however, that for nanocomposite substoichiometric alloy ribbons (compositions in the series Pr-10(Fe100-xCox)(84)B-6, x=0-40) the second quadrant hysteresis loop shapes for overquenched and annealed ribbons were generally poor and, even though J(r) was still substantially enhanced (in the range 0.95-1.05 T), the intrinsic coercivities H-i(c) were disappointingly low (275-450 kA/m). Substitution of 1 at. % Zr for Fe in the Pr10Fe84B6 alloy, nevertheless, resulted in an improved loop shape and H-i(c) (525-550 kA/m), with (BH)(max) increased to 130-140 kJ m(-3) (compared with 80- 110 kJ m(-3) for the Zr-free alloys). (C) 2000 American Institute of Physics. [S0021-8979(00)51408-X].