Interface effects on magnetostriction in pulsed laser deposited Co/Fe/Co cylindrical soft magnetic multilayers

Amorphous-nanocrystalline Co/Fe/Co soft magnetic multilayers were deposited by a pulsed laser. The thickness of the Co layers was constant at 18.7 nm for each layer and the Fe layer was varied between 0 and 110 nm. The spontaneous magnetization of the films was proportional to the Co and Fe layer thicknesses. Their isotropic saturation magnetostriction coefficients (lambda(S)) were determined. The lambda(S) changed from negative to positive values depending on the thickness of the Fe layer. The magnetostriction of the multilayers was greater than what would be expected from the proportional superposition of lambda(S)(Co) and lambda(S)(Fe) in the interval 0 <= x <= 50 at.% Fe. The maximum magnetostriction deviation was seen at an iron content of approximate to 26%. The larger experimental magnetostriction values are explained by an interface contribution, in which Fe and Co atoms diffuse into the adjacent layers. Assuming this interface contribution is due to the formation of two layers of Fe50Co50 in the trilayer structure, we were able to calculate the thickness and the magnetostriction coefficient of each interdiffusion layer, t(FeCo) = (1.4 +/- 0.3) nm and lambda(S)(FeCo) = +(240 +/- 10) x 10(-6).