Proximity Induced Superconductivity in Ferromagnetic Nanowires: Magnetoresistance Oscillations and Steps in I-V Characteristics

Ferromagnetic order requires electronic spins to be aligned parallel whereas singlet superconducting order requires spins to be aligned antiparallel. This spin incompatibility limits the superconducting proximity effect to $\sim $1 nm in bulk ferromagnets. In ferromagnetic nanowires contacted with superconducting W electrodes however, the proximity effect is seen to extend to $\sim $ 400 nm [Wang et al., Nat. Phys. 6, 389 (2010)]. The mechanism behind the long range proximity in these systems is not certain. We have studied single crystalline Co nanowires contacted with normal electrodes with a single superconducting W strip patterned on the nanowire. The long range proximity effect is found to persist in this geometry. Robust magnetoresistance oscillations were found when an external field parallel to the axis of the wire was applied. In addition, regularly spaced peaks were seen in the dI/dV vs. V characteristics of the sample. The origin of the oscillations and the peaks is not understood.