Microstructure, crystallization behavior, and soft magnetic properties of Co-doped Finemet-type nanocrystalline alloys

(Fe74Si15B7Cu1Nb3)(100-x)Co-x (x = 0, 2, 4, 6, 8, and 10) nanocrystalline alloys prepared by melt spinning were investigated. The results indicate that the saturation magnetic flux density (B-s) of these alloys could be efficiently enhanced from 1.29 to 1.40 T, accompanying with good soft magnetic properties. Glass-forming ability of these alloys decreased with increasing Co content, whereas the temperature interval (& UDelta;T-x = T-x2 - T-x1) increased significantly. The coercivity (H-c) of these alloys almost keep constant in a wide annealing temperature range. Crystallization kinetics shows that the activation energy of the alloy decreases with the increment of Co content, implying the nucleation and growth of & alpha;-Fe(Co) grains become easier. Microstructural analysis indicates that the mean grain size of the & alpha;-Fe(Co) grains increases gradually with increasing Co content. Irregular and disorder domain walls observed on the ribbon surface may originate from the pinning effects of surface crystallites, resulting in the deterioration of soft magnetic properties.