Resistive transitions in Nb/Cu$_{0.41}$Ni$_{0.59}$/Nb trilayers

The superconducting phase transition in ${\rm Nb/Cu_{0.41}Ni_{0.59}/Nb}$ trilayers, with superconducting (S) Nb and ferromagnetic (F) ${\rm Cu_{0.41}Ni_{0.59}}$, has been experimentally studied as function of the F-layer thickness by measuring the temperature dependence of the electrical resistance $R(T)$. It is shown that the shape and the width of the $R(T)$ curves depends on the ${\rm Cu_{0.41}Ni_{0.59}}$ thickness, in particular in the regime where $\pi-$coupling between the S-layers can be expected. To explain the data we developed a qualitative model which makes the interconnection between the superconducting phase transition and the 0 to $\pi$ transition in SFS structures more evident.