Spin injection and spin accumulation in Permalloy-Copper mesoscopic spin valves

We study the electrical injection and detection of spin currents in a lateral spin valve device, using permalloy (Py) as ferromagnetic injecting and detecting electrodes and copper (Cu) as nonmagnetic metal. Our multiterminal geometry allows us to experimentally distinguish different magnetoresistance signals, being (1) the spin valve effect, (2) the anomalous magnetoresistance (AMR) effect, and (3) Hall effects. We find that the AMR contribution Of the Py contacts can be much larger than the amplitude of the spin valve effect, making it impossible to observe the spin valve effect in a "conventional" measurement geometry. However, these "contact" magnetoresistance signals can be used to monitor the magnetization reversal process, of the spin injecting and detecting Py contacts. In a "nonlocal" spin valve measurement we are able to completely isolate the spin valve signal and observe clear spin accumulation signals at T = 4.2 K as well as at room temperature. We obtain spin diffusion lengths in Cu. of 1 Am and 350 nm. at T = 4.2 K and room temperature respectively.