Origin of low coercivity of (Fe_0.75B_0.15Si _0.10)_100-xNb_x(x=1-4) glassy alloys

The density and the magnetization process of the melt-spun (Fe0.75 B0.15 Si0.10) 100-x Nbx (x=1-4) glassy alloys have been investigated to clarify the origin of low coercivity (Hc). Both Hc and the difference of the densities between the crystalline and glassy phases, which corresponds to the free volume in the glassy phase, decrease with increasing Nb content. An analysis of the magnetization process based on the law of approach to ferromagnetic saturation reveals that quasidislocation dipole (QDD)-type defects are the main sources of elastic stress. The results also suggest that the pinning force for magnetic domain walls generated by one QDD-type defect is independent of the Nb content, but the number density of QDDs decreases with increasing the Nb content. Therefore, it concluded that the origin of low Hc of the glassy alloys is the low number density of QDDs which corresponds to the low number density of the domain-wall pinning sites.