Measurement of resistance and spin-memory loss (spin relaxation) at interfaces using sputtered current perpendicular-to-plane exchange-biased spin valves

We describe measurements using a technique for determining interfacial resistances and loss of spin-direction memory (spin relaxation) for nonmagnetic metals and nonmagnetic interfaces. The technique involves inserting the metal of interest, or a multilayer, into the middle of a current-perpendicular (CPP) permalloy-based exchange-biased spin-valve and monitoring the resulting increase in CPP resistance and decrease in magnetoresistance. The technique has the advantage over earlier ones of giving both uniform current and control of the required magnetic states. We test and validate the technique using (a) an alloy, CuPt (6 at. %), in which the spin-diffusion length has previously been measured with a different technique, (b) a metal, Ag, where we expect a long spin-diffusion length, and (c) Cu/Ag interfaces, where we expect little if any spin-memory loss. We then use the technique to measure spin-memory-loss (the spin-diffusion length) at 4.2 K of the antiferromagnetic alloy FeMn, which is used for pinning the ferromagnetic layers in our spin-valves, and of sputtered single layers of V, Nb, and W preparatory to measuring interfacial resistance and interfacial spin-memory loss in sputtered $[\mathrm{C}\mathrm{u}/\mathrm{A}\mathrm{g}{]}_N,$ $[\mathrm{C}\mathrm{u}/\mathrm{V}{]}_N,$ $[\mathrm{C}\mathrm{u}/\mathrm{N}\mathrm{b}{]}_N,$ and $[\mathrm{C}\mathrm{u}/\mathrm{W}{]}_N$ multilayers with N repeats. To our surprise, we discovered large interfacial spin-relaxation rates for V/Cu, Nb/Cu, and W/Cu interfaces. These rates seem to be understandable as due to spin-orbit coupling in high resistivity interfacial alloys.