Angular dependence of the upper critical field in Nb/CuMn multilayers

We present data related to the temperature $(T)$ and angular ({θ}) dependencies of the upper critical field (Hc2) of Nb(superconductor)-CuMn(spin glass) multilayers as a function of CuMn layer thickness and Mn concentration. We observe two-dimensional (2D) behavior for large CuMn thickness. As the CuMn layer thickness is decreased, the Hc2(T) curves correspond to three-dimensional (3D) behavior, while the Hc2(θ) dependencies measured in the range [-1.5^∘,+1.5^∘] are more sensitive to the dimensionality of the system. In particular, the experimental data reveal a 3→D2D crossover at very low angle when the Mn percentage is increased at fixed CuMn thickness. This behavior can be related to vortex dimensionality change in anisotropic superconductors.