[en] Annealing of the (1.1 nm Co₉₀Fe₁₀/2.2 nm Cu)x20 and (1.1 nm Co₉₀Fe₁₀/2.2 nm Cu₈₅Ag₁₀Au₅)x20 multilayers at 235 deg. C improved their magnetoresistance as compared to the virgin samples. Annealing at higher temperatures resulted in degradation of the magnetoresistance effect. This observation raised the motivation of a detailed structural study using small-angle X-ray scattering, wide-angle X-ray diffraction, electron diffraction and transmission electron microscopy with the aim to link the structural changes in the system to the changes in the magnetoresistance. The structure studies have shown that the maximum of the magnetoresistance observed after annealing at 235 deg. C is related to the separation of Co₉₀Fe₁₀ and Cu, which are partly intermixed at interfaces after the deposition process. The decay of the GMR effect at higher annealing temperatures is caused by an increase of the interface roughness, which led in the Co₉₀Fe₁₀/Cu multilayers to occurrence of non-continuous interfaces and to short-circuiting of magnetic layers. In the Cu₈₅Ag₁₀Au₅ multilayers, the combination of small-angle X-ray scattering and wide-angle X-ray diffraction has shown that Cu₈₅Ag₁₀Au₅ did not form an alloy with the nominal composition: Only a part of Au and Ag was dissolved in the copper structure; the remainder of Ag and Au formed precipitates