Spin polarization in ferromagnet/insulator/superconductor structures with the superconductor on top of the barrier

The tunneling spin polarization (TSP) in ferromagnet/insulator/ superconductor (FIS) sandwich was investigated using superconducting tunneling spectroscopy (STS). Similar values of TSP were observed in Co-Fe alloys in optimally prepared sandwiches. TSP measurement of pure Ni and Ni-fe alloys was more susceptible to reaction with barrier such that TSP was lower when ferromagnet was grown under tunnel barrier. The results show dependence of tunneling magnetoresistance (TMR) in magnetic tunnel junctions.