Abstract
Critical supercurrents, I c in Nb Cu 1− x Ni x Nb Josephson SFS junctions with F-layers prepared from ferromagnetic Cu 1− x Ni x alloys have been studied. For value x =0.52 and particular F-layer thickness we have observed I c ( T ) oscillations with I c vanishing for some values of T . We associate this reentrant superconducting behavior with a crossover of the SFS junction from ‘0’- to ‘π’-state that is related to temperature dependence of spatial oscillation period of induced superconducting order parameter in the weak ferromagnet. We argue this is the first experimental evidence of the π-behavior of a Josephson junction, that is the special feature of superconducting pair flow through a ferromagnet predicted for SFS junctions by Bulaevskii, Buzdin et al [1].
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