The interfacial structure and degradation mechanism of the GMR effect in Co90 Fe10/Cu and Ni70Co30/Cu magnetic multilayers

We investigated the microstructures of Co90Fe10/Cu and Ni70Co30/Cu multilayers before and after annealing at 285 deg. C for 2 h, as well as the influence of microstructures on the thermal degradation of the GMR (giant magnetoresistance) effect, using innovative x-ray anomalous scattering techniques. It is found that there exists a significant asymmetry between the interfaces on both sides of the Cu layers during the deposition. The diffusion only occurs at the Cu/Ni70Co30 and Cu/Co90Fe10 interfaces while the Ni70Co30/Cu and Co90Fe10/Cu interfaces are sharp. After annealing at 285 deg. C, the Co90Fe10/Cu interface is still sharp, but the Ni70Co30/Cu interface forms a CuNi2Co intermixing region. X-ray diffuse scattering profiles performed with x-ray energy close to the Fe, Co, Ni and Cu K edges show that the local lateral environments of Fe, Co, Ni and Cu at the interfaces are different for both the as-deposited multilayers. After annealing, the interfacial lateral correlation lengths and the fractal exponent of the Ni70Co30/Cu multilayer decrease significantly and the difference of the interfacial lateral correlation lengths of Co, Ni and Cu becomes smaller. However, those of the Co90Fe10/Cu multilayer do not change. This indicates that the main cause of thermal degradation of the GMR effect is the compositional intermixing at the multilayer interface, which has more influence on the GMR effect than the atom diffusion along the grain boundary