Thermally induced modification of GMR in Co/Cu multilayers: correlation among structural, transport, and magnetic properties

Co/Cu multilayers with individual layer thickness corresponding to the second maximum of the antiferromagnetic coupling were investigated as an attractive system for applications utilizing the giant magnetoresistance (GMR). Annealing causes distinct changes in the transport and magnetic properties of the multilayers. To obtain a deeper understanding of the triggering mechanisms, the variations in the layer and lattice structure occurring during heat treatment were studied by x-ray diffraction and electron microscopy. Structural and corresponding magnetic changes were observed according to characteristic temperature regions. The initial GMR of about 25% increased up to an annealing temperature of 400°C in correlation with the sharpening of the interfaces. Above 300°C grain growth sets in, and high coherency strains give rise to a transition from a ⟨111⟩ to a ⟨100⟩ texture. Above an annealing temperature of 400°C increasing layer defects cause a reduction of the GMR, and exceeding 600°C results in a complete transition from the multilayer configuration to a granular-like structure with large (∼100 nm) domains of Co and Cu.