Current distribution inside Py/Cu lateral spin-valve devices

We have investigated experimentally the nonlocal voltage signal (NLVS) in the lateral Permalloy (Py)/Cu/Py spin-valve devices with different width of Cu stripes. We found that NLVS strongly depends on the distribution of the spin-polarized current inside Cu strip in the vicinity of the Py detector. To explain these data we have developed a diffusion model describing spatial (three dimensional) distribution of the spin-polarized current in the device. The results of our calculations show that NLVS is decreased by a factor of 10 due to spin flip scattering occurring at the Py/Cu interface. The interface resistivity on the Py/Cu interface is also present, but its contribution to reduction of NLVS is minor. We also found that most of the spin-polarized current is injected within the region 30 nm from the Py injector/Cu interface. In the area at Py detector/Cu interface, the spin-polarized current is found to flow mainly close on the injector side, with 1/e exponential decay in the magnitude within the distance 80 nm.