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

We present data related to the temperature (T) and angular (theta) dependencies of the upper critical field (H-c2) 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 H-c2(T) curves correspond to three-dimensional (3D) behavior, while the H-c2(theta) dependencies measured in the range [-1.5 degrees, + 1.5 degrees] an more sensitive to the dimensionality of the system. In particular, the experimental data reveal a 3D --> 2D 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.