We study spin accumulation in an aluminium island, in which the injection of a spin current and the detection of the spin accumulation are done by means of four cobalt electrodes that connect to the island through transparent tunnel barriers. Although the four electrodes are designed as two electrode pairs of the same shape, they nonetheless all exhibit distinct switching fields. As a result the device can have several different magnetic configurations. From the measurements of the amplitude of the spin accumulation, we can identify these configurations, and using the diffusion equation for the spin imbalance, we extract the spin relaxation length $lambda_mathrm{sf} = 400 pm 50$~nm and an interface spin current polarization $P = (10 pm 1)%$ at low temperature and $lambda_mathrm{sf} = 350 pm 50$~nm, $P = (8 pm 1)%$ at room temperature.
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