Effect of Frozen Magnetic Flux on the Electrical Transport Characteristics of Superconductor-Ferromagnet Junction.

We studied electrical transport characteristics of lateral superconductor (SC)-ferromagnet (FM)-superconductor devices which were found to exhibit two strikingly different differential resistance states at zero field. The key difference between these states is that the critical current ( I) is dramatically lower for one state (state 2) than the other (state 1). Moreover, state 2 exhibits a higher zero bias resistance than state 1. We explain this as an effect of magnetic field from the frozen flux in SC on the Andreev reflection process at the SC-FM interface. The magnetoresistance (MR) curves at different dc current biases are nonhysteretic and symmetric with respect to zero field axis when the device is at state 1. In contrary to this, MR curves at state 2 are asymmetric and show a pronounced hysteresis at high bias current. These effects indicate a coupling between applied field and frozen flux, which affects the transport characteristics of the SC-FM interface. [ABSTRACT FROM AUTHOR]