Magnetic properties and short-range order in Co-Nb-B alloys

The saturation magnetizations, crystallization temperatures, and thermomagnetic curves of various Co-rich Co-Nb-B glasses are presented. The saturation magnetizations and the phases of the crystallized specimens are also reported. A scanning transmission electron microscopy study on one of the glasses revealed no gross chemical phase separation. A model for the magnetic moments of a Co-$T_E$-M system is developed, with the use of Cowley’s short-range order parameters, that is based on the coordination number of Co atoms around the early-transition-metal ($T_E$) and metalloid (M) atoms. Application of the model to the moment data shows that the coordination numbers around the Nb and B atoms in the glasses are 12 and 6, respectively, and that the Nb and B atoms have a tendency to cluster around each other. The moment difference between the crystalline and glassy samples may have been caused by ${\mathrm{Co}}_3$Nb Laves-type phases present in the former, rather than by chemical phase separation in the latter.