Spin-Reflective Metallic Cu/Cr Interface*

Electrically conductive metals are typically good transmitters or absorbers of pure spin currents. Here, we report evidence that an interface of two conductive elemental metals – namely, Cu and Cr– constitutes a good spin-current reflector. Using frequency-dependent and element-sensitive spin pumping methods, we have measured spin-current transport normal to NiFe/Cu/Cr(t_Cr)/(Co)Fe stacks with various Cr thicknesses t_Cr. With t_Cr just a few nm, our results demonstrate that both transmission and absorption of spin-current across Cu/Cr are suppressed – that is, the spin current is largely reflected by the Cu/Cr spacer. Complementary measurements show sizable spin transmission through a Cr spacer not interfaced with Cu, thus indicating the Cu/Cr interface – rather than the Cr bulk – to be the source of the strong spin reflection. Further, we find that this peculiar spin-reflective behavior does not originate from the antiferromagnetism of Cr. Our findings point to the possibility that a broad variety of metallic bilayers can form effective spin reflectors, thereby offering new avenues in the fundamental studies and engineering of pure spin currents in multilayers.