Magnetostriction as important quantity in transformations of Fe73.5−x NixCu1Nb3Si13.5B9 finemets into nanocrystalline phases

Nanocrystallization in Fe73.5−x NixCu1Nb3Si13.5B9 rapidly quenched system, x=0, 10, 20, 30, and 40, in form of ribbons was investigated by measurements of magnetostriction λS. Using direct magnetostriction measurement method the magnetostrictions as functions of external magnetic field in parallel and perpendicular directions, λ∥ (H) and λ⊥(H), were determined and the values of saturation magnetostriction λS(H), volume magnetostriction ω(H) and isotropic force magnetostriction ∂ω/∂H were calculated. The values of λS for different stages of transformation were compared with those on ribbon and bulk α-Fe(Si), Fe3Si, Fe3B, Fe2B, Fe3NiSi1.5, which represent the crystalline phases formed during crystallization. The dependencies of magnetostrictions λ∥ (H) and λ⊥(H) in amorphous Finemet samples and in pure Fe and Ni lead to conclusions about the existence and quantity of clusters with increased content of Fe and Ni. The shape and magnitude of λ∥ (H), λ⊥(H), λS, ω(H), and ∂ω/∂H obtained at different transformation stages by isochronal annealing and the corresponding dependencies obtained on ribbon polycrystalline reference samples provide information about the percentual content of grains with different compositions contributing to the total magnetostriction effect.