The superconducting critical temperature ($T_c$) of ferromagnet-superconductor-ferromagnet systems has been predicted to exhibit a dependence on the magnetization orientation of the ferromagnetic layers such that $T_c^{\mathrm{A}\mathrm{P}}>T_c^P$ for parallel ($P$) and antiparallel (AP) configurations of the two ferromagnetic layers. We have grown $\mathrm{C}\mathrm{u}\mathrm{N}\mathrm{i}/\mathrm{N}\mathrm{b}/\mathrm{C}\mathrm{u}\mathrm{N}\mathrm{i}$ films via magnetron sputtering and confirmed the theoretical prediction by measuring the resistance of the system as a function of temperature and magnetic field. We find an $\sim 25\%$ resistance drop occurs near $T_c$ in ${\mathrm{C}\mathrm{u}}_{0.47}{\mathrm{N}\mathrm{i}}_{0.53}(5\mathrm{n}\mathrm{m})/\mathrm{N}\mathrm{b}(18)/\mathrm{C}\mathrm{u}\mathrm{N}\mathrm{i}(5)$ when the two CuNi layers change their magnetization directions from parallel to antiparallel, whereas there is no corresponding resistance change in the normal state.

• Received 15 May 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.267001