The influence of partial replacement of Fe by Co in FeCoCuNbSiB alloys on magnetic properties.

Crystallization process and magnetic properties of the Fe73.5-xCoxCu1Nb3Si13.5B9 alloys (x=0, 10, 20, 30, 40, 50.8, 73,5) were investigated. The structure of partially crystalized alloys was examined by X-ray diffractometry (XRD). The magnetic properties (coercivity Hc and magnetostriction constant pi s) of the alloys after heat treatment conducted at optimal temperature for 1 h in Ar atmosphere were measured at room temperature. It was found that the optimal annealing temperature, at which the best magnetic properties are obtained, decreases with the increase of Co content. For the x values up to 40, an increase of coercivity with x was observed, corresponding to the increase of the mean grain size of the alfa-FeSi(Co) crystallites. However, at x=50, a noticeable magnetic softening was observed, but above x=50, coercivity of the nanocrystalline alloys rapidly increased, which is correlated with the magnetic decoupling of alpha-FeSi(Co) crystallites. At the optimal annealing temperature, the maximum magnetostriction coefficient pi s, is observed for the alloy with x=20.