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

Abstract

We present data related to the temperature $\mathrm{}\left(T\right)\mathrm{}$ and angular (θ) dependencies of the upper critical field ${(H}_{c2\mathrm{}})$ 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 $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ curves correspond to three-dimensional (3D) behavior, while the $H_{c2\mathrm{}}\left(\theta \right)$ dependencies measured in the range $[-1.5°,+1.5\mathrm{}°]$ are more sensitive to the dimensionality of the system. In particular, the experimental data reveal a $3\overrightarrow{D}2\mathrm{D}$ 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.