Optimization of permanent magnetic properties in melt spun Co82−xHf12+xB6 (x = 0–4) nanocomposites

Abstract

Magnetic properties of melt spun Co82−xHf12+xB6 ribbons made with various wheel speeds have been studied. The ribbons with x = 0–1 are not easy to crystallize and thus display soft magnetic behavior even at wheel speed of 10 m/s. In contrast, the ribbons with x = 1.5–4 at optimized wheel speed exhibit good permanent magnetic properties of Br = 0.41–0.59 T, iHc = 120–400 kA/m, and (BH)max = 10.6–48.1 kJ/m3. The optimal magnetic properties of Br = 0.59 T, iHc = 384 kA/m, and (BH)max = 48.1 kJ/m3 are achieved for Co80Hf14B6 ribbons at wheel speed of 30 m/s. X-ray diffraction, thermo-magnetic analysis, and transmission electron microscopy results show that good hard magnetic properties of Co82−xHf12+xB6 ribbons (x = 2–4) are originated from the Co11Hf2 phase well coupled with the Co phase. The change of magnetic properties for Co82−xHf12+xB6 ribbons spun at various wheel speeds is correlated to microstructure and phase constitution. The strong exchange-coupling effect between magnetic grains for the ribbons with x = 2–3 at wheel speed = 30 m/s leads to remarkable permanent magnetic properties. The presented results suggest that the optimized Co82−xHf12+xB6 (x = 2–3) ribbons are much suitable than others (x = 0–1.5 and 4) for making rare earth and Pt-free magnets.