Bias Current Dependence of Superconducting Transition Temperature in Superconductor/Spin-Valve Nanowires

Superconductor/ferromagnetic (S/F) heterostructures have been a focus of intensive research over the past two decades. Apart from their importance for understanding of fundamental physics of the superconducting proximity effect, S/F nanostructures may find applications in low-power cryogenic computing. Competition between superconducting and ferromagnetic ordering in S/F heterostructures can lead to unusual types of magneto-transport effects emerging from the proximity effect at the S/F interfaces. One example is the spin switch effect observed in S/F/F spin valves near the superconducting transition temperature T_c.
Here we present an experimental study of current-in-plane magneto-resistance (MR) in Nb/Co/Cu/Co/CoO nanowires as a function of the bias current near the T_c of the multilayer. These measurements reveal an unexpected dependence of the MR on the bias current. We attribute this interesting result to spin Seebeck current injection from the Co/Cu/Co spin valve into the Nb layer driven by a temperature gradient perpendicular to the multilayer plane that arises from Ohmic heating of the layers. We will present detailed measurements of the magnitude of this effect as a function of bias current and the thickness of the free magnetic layer.