Magnetoresistance transformation observed in Fe/Mo multilayers prepared by electron beam evaporation

Fe/Mo multilayers were prepared by electron beam evaporation. The magnetoresistance (MR) properties of the multilayers changed significantly with the thickness of Mo layers in the films. When the thickness of nonmagnetic Mo layers reached 3.0 nm, the MR effect of the multilayers transformed from a negative to a positive one. The curve of MR is easily saturated at relatively low applied magnetic fields. The MR ratio of [Fe(1.5 nm)/Mo(1.0 nm)]42 multilayers with a typical negative MR effect can reach an absolute value of 0.1%, and that of [Fe(1.5 nm)/Mo(5.0 nm)]15 multilayers with a typical positive MR effect can reach a value of 0.42%. Antiferromagnetic interlayer coupling can be observed in our films at room temperature. The origin of the MR variation is discussed according to three contributions, i.e. ordinary MR, induced by Lorentz force, anisotropic MR and the MR induced by spin-dependent scattering between the interfaces of the magnetic-nonmagnetic layers