Magnetostrictions of CoFe sensoring layers in spin valves

The effective magnetostriction (λ_s) of ultrathin CoFe sensor layers has been measured as a function of CoFe and spin-filter nonmagnetic layers over the range from 1.0 to 3.0 nm. The λ_s shows an anomalous variation at thicknesses of interest and disagrees with the expectation of the Ne´el model, where the surface/interface contribution is supposed to lead to observation that the λ_s varies with the well-known reciprocal law of magnetic layer thickness. Within the framework of a coherent strain model proposed herewith, both the deviation of magnetostriction behavior from the reciprocal law and its nonmagnetic layer structure dependence are satisfactorily explained. The interface-induced magnetoelastic coupling, laminated structure dependent strains, and stresses are called for in explaining the magnetostriction of magnetically soft sensor layers.