Anti-Lenz Supercurrents in Superconducting Spin Valves

Here, we present a study on Si(111)/Ta(150 angstrom)/IrMn(150 angstrom)/NiFe(50 angstrom)/Nb(x)/NiFe(50 angstrom)/Ta( 50 angstrom) spin valves with x = 100-500 angstrom A. Samples with a Nb layer thickness of 300 angstrom or higher exhibit an unusual magnetization behavior below Tc. The superconducting Nb layer contributes strongly to the magnetization, and manifests itself in an anomalous hysteresis loop. While the hysteresis loop is seemingly similar to what is generally expected from hard superconductors and many superconductor/ferromagnet hybrid systems, its direction is invertedwhen compared towhat is generally observed. Thus, the samples show paramagnetic behavior for upsweeping fields and diamagnetic behavior for downsweeping fields. This means that the respective samples exhibit a magnetization, which is contrary to what Lenz's rule dictates.