Active supercurrent control in superconductor/ferromagnet heterostructures

Several recent papers predict that the critical temperature of superconducting/ferromagnet heterostructure can be controlled by varying the exchange field of the ferromagnet within the superconductor, providing a means of controlling the superconducting properties. This paper reports the first experimental observation of this effect: we show that the critical temperature and critical current of a Nb/Co bilayer can be controlled by a small magnetic field, on the order of a few tens of kA/m. In these devices, the suppression of T_c is minimised at the coercive field of the Co layer implying that with a sufficiently fine domain structure the net exchange field in the superconductor is reduced. These structures offer the potential for active control of the superconducting properties in both low and high T_c materials through the application of very small magnetic fields