Magnetoresistance and magnetostriction of Ni81Fe19 and Co90Fe10 mono- and bilayer films

Monolayer and bilayer films of Ni81Fe19, Co90Fe10, Co90Fe10/Ni81Fe19, and Ni81Fe19/Co90Fe10 have been grown on thermally oxidized Si. The magnetoresistance (MR) of the samples was measured as a function of applied DC magnetic field, using a four-point probe method. The magnetostriction constant, λs, was derived from the change of anisotropy field as a function of strain. The dependence of the MR on different combinations of film layers was investigated. The magnetoresistance of the bilayers changed dramatically upon reversal of the layer order. The mono- and bilayer samples with the same material on top of the substrate showed similar MR loop shapes. However, the saturation fields of the bilayers were larger than those for the monolayers. The magnetostriction of all samples was negative. We discuss the consequences for the study and optimization of spin-valve devices.