Active supercurrent control in superconductor/ferromagnet heterostructures

Several recent papers predict that the critical temperature of superconduct ing/ferromagnet heterostructure can be controlled by varying the exchange f ield of the ferromagnet within the superconductor, providing a means of con trolling the superconducting properties. This paper reports the first exper imental observation of this effect: we show that the critical temperature a nd critical current of a Nb/Co bilayer can be controlled by a small magneti c field, on the order of a few tens of kA/m, In these devices, the suppress ion 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 su perconductor is reduced. These structures offer the potential for active co ntrol of the superconducting properties in both low and high T-c materials through the application of very small magnetic fields.