Magnetic properties, phase evolution, and coercivity mechanism of CoxZr98−xB2 (x=74−86) nanocomposites

Magnetic properties, phase evolution, and coercivity mechanism of melt-spun CoxZr98−xB2 (74⩽x⩽86) nanocomposites were studied systematically. From x-ray diffraction analysis, nearly single magnetic phase, Co23Zr6, is found in Co74Zr24B2 ribbon (x=74). With increasing Co content x, an additional phase, Co5Zr, is found for x=76; two phases, namely, fcc Co and Co5Zr, are found for x=78−84, but fcc Co is the only phase that can be detected in ribbon with x=86. The optimal magnetic properties of Br=5.13kG (σr=49emu∕g), Hci=4.1kOe, and (BH)max=5.1MGOe are obtained in Co80Zr18B2 ribbons quenched at Vs=45m∕s, which possesses Co5Zr and minor fcc-Co phases with nanoscale grain size (∼50 and ∼20nm, respectively). Strong exchange-coupling effect occurred between grains as evidenced by the Henkel plot, giving rise to the improvement of remanence and magnetic energy product. The coercivity of CoxZr98−xB2 nanocomposites is mainly governed by reverse domain nucleation mechanism.