Saturation magnetostriction of an ultrathin CoFe free-layer on double-layered underlayers

We investigated the saturation magnetostriction (lambda(s)) of an ultrathin CoFe free-layer on double-layered underlayers of Ru/Cu. By increasing the Ru underlayer thickness, lambda(s) becomes positively large; on the other hand, lambda(s) becomes negatively large by increasing the Cu underlayer thickness. This tendency can be explained by the model where lambda(s) is changed by the film strain. The lambda(s) sensitivity on the Cu underlayer thickness becomes large with increasing the Co concentration of the CoFe free-layer. This indicates that CoFe lambda(s) becomes sensitive to strain with increasing Co concentration. In order to realize small magnetostriction spin-valve films with an ultrathin CoFe free-layer, we have to take care of the lattice strain of the film. (C) 2002 American Institute of Physics.