Giant magnetoresistance in Co/Cu multilayers with Co layers of alternating thicknesses: Reduction of magnetoresistive hysteresis

A description is given of the magnetoresistive properties of Co/Cu multilayers in which the thicknesses of antiferromagnetically coupled Co layers are alternated between two values. With such an arrangement, the thicker Co layers are coupled more strongly to applied magnetic fields than are the thinner Co layers. Consequently, one may attain conditions where the magnetization direction of the thinner Co layers is the result of a balance between the applied magnetic field and an antiferromagnetic coupling to the adjacent thicker Co layers, whose magnetization direction is dominated by the applied magnetic field. With specimens whose Cu spacer-layer thickness is 9 Å (i.e., at the first antiferromagnetic maximum) the dependence of total magnetization on applied magnetic field reveals the different behavior of the two types of Co layer. This behavior may be exploited to obtain materials with reduced magnetoresistive hysteresis at the second antiferromagnetic maximum (i.e., with Cu spacer thickness of 20 Å) by combining the large magnetoresistance of Co layers with thicknesses ∼15 Å with the small hysteresis of Co layers with thicknesses ∼3 Å.