Yukai An, Bo Dai, Hongdi Zhang, Zhenhong Mai, Jianwang Cai, Zhonghua Wu

The interfacial structure and degradation mechanism of the GMR effect in Co₉₀Fe₁₀/Cu and Ni₇₀Co₃₀/Cu magnetic multilayers

Journal of Physics D 39 (2006) 1711–1717

We investigated the microstructures of Co₉₀Fe₁₀/Cu and Ni₇₀Co₃₀/Cu multilayers before and after annealing at 285 °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 °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.

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