Interface governed magnetostrictionin ultra thin CoFe and Fe films

摘要

Two different types of polycrystalline films, films with low (Fe) and films with high (Co_(50)Fe_(50)) saturation magnetostriction lambda _s were sandwiched between Cu to study the thickness dependence of lambda _s in Cu/X/Cu system. We utilised a new method (ROTMOKE) for a high accurate H_k determination. The values for lambda _s were determined by analysing the change of K_k during application of compressive and tensile stress by cylindrical bending of the substratejoint with the film. For both systems, a remarkable contribution of the interface to the lambda _s was found. The sign of the interface contribution is opposed to the sign of bulk lambda _s leading to a zero transition of lambda _s. For Fe this transition occurs at a thickness of 5 nm whereas for the CoFe film with a strong lambda _s value of the bulk of around 80 centre dot 10~(-6) a transition was extrapolated at a thickness around 1 nm.