Dimensional crossover and flux pinning of decoupled Cu₅₀Ni ₅₀/Nb multilayers

The behaviors of superconducting transition temperature Tc and upper critical field Hc2 as a function of different superconductor thicknesses have been investigated in Cu50 Ni50 Nb trilayers and multilayers. We deduced superconductor critical thickness, below which superconductivity vanishes, by analyzing the data in terms of proximity theory. The temperature dependence of Hc2 measurement reveals the spatial dimensional crossover and the flux pinning mechanism in the superconductor. A strong pair-breaking effect was observed in the weak ferromagnetic Cu50 Ni50 layers from both measurements. We attribute our observation to the high interface transparency between Cu50 Ni50 and Nb.