Magnetostriction and Young's modulus of [Fe15Ni85/Fe25Ni75] multilayers

A series of ferromagnetic [AxB60−x]2 multilayers, where A=Fe15Ni85, B=Fe25Ni75, and x is the thickness of layer A in nanometer, were manufactured by the vapor evaporation method. Three measurements were carried out on each sample: the Auger depth-profile analysis, a measurement of Young's modulus Ef by the nano-indentation system, and the measurement of saturation magnetostriction λs by the optical-cantilever system. Bulk and thin-film samples have different Young's modulus, and, moreover, in the multilayer, the modulus Ef becomes a nonlinear function of x. A set of λs data derived using the measured Ef is compared with data based on the bulk value Ef=2.0×1011 N/m2. The deposition temperature here is Ts=200 °C. With increasing Ts (here up to 400 °C), the interfacial mixing increases as well. The deviation Δλs of magnetostriction from theoretically predicted linear behavior is found to be oscillatory at low Ts (where Δλs changes signs), but monotonic at high Ts (where Δλs maintains the same sign). A qualitative explanation of these phenomena is provided.