Magnetic properties improvement of melt spun Co 86.5 Hf 11.5 B 2 nanocomposites by refractory elements substitution

Abstract Magnetic properties of melt spun Co 86.5 Hf 10.5 MB 2 ribbons with refractory elements substitution (M=Cr, Nb, Ti, Zr) have been studied. For ternary Co 86.5 Hf 11.5 B 2 ribbon, permanent magnetic properties of B r =0.71 T, i H c =192 kA/m, and (BH) max =34.4 kJ/m 3 are obtained, and they are significantly improved to B r =0.73–0.76 T, i H c =136–216 kA/m and (BH) max =38.4–52.8 kJ/m 3 with M substitution. Summarized with the results of x-ray diffraction refinement, thermal magnetic analysis, and transmission electron microscopy, the Co 86.5 Hf 10.5 MB 2 nanocomposites following the optimal crystallization treatment mainly consist of orthorhombic 7:1 and face-center-cubic Co phases. Fine microstructure with average grain size in the range of 12.5−19.6 nm promotes exchange coupling effect between magnetic grains, thus improving permanent magnetic properties. The magnetic field dependence of coercivity reveals that coercivity of the studied Co 86.5 Hf 10.5 MB 2 nonocomposites is mainly governed by the reverse domain nucleation mechanism.