Spin-diffusion lengths of Cu1-xNix using current perpendicular to plane magnetoresistance measurements of magnetic multilayers

Spin-relaxation effects are generally believed to have a strong influence on giant magnetoresistance of ferromagnetic/noble-metal multilayers. We have measured current perpendicular to plane magnetoresistances (CPP MR's) of sputtered Co/Cu1-xNix multilayers with x=0.06, 0.10, 0.14, and 0.23. Our results indicate that the spin-diffusion length of CuNi is reduced as the concentration of Ni increases. Spin-diffusion lengths obtained from fitting the CPP MR to Valet-Fert theory are in a good agreement with theoretical calculations from spin-orbit scattering. Assuming that the permalloy(Py)-Cu interface in Py/Cu multilayers resembles a CuNi alloy, we can conclude that there will be spin-flip scattering at a Py-Cu interface, but we expect its effect on the MR to be small.