Spin accumulation probed in multiterminal lateral all-metallic devices

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 ${\lambda }_{\mathrm{sf}}=400\pm 50\mathrm{nm}$ and an interface spin current polarization $P=(10\pm 1)\%$ at low temperature and ${\lambda }_{\mathrm{sf}}=350\pm 50\mathrm{nm}$, $P=(8\pm 1)\%$ at room temperature.

Figure 1

Scanning electron microscope (SEM) image of the device. Visible are the Al island and the four Co contacts of two different widths: the wider electrodes connecting the island at its ends, have a lower switching field. In the nonlocal measuring configuration, a current $I$ is injected from Co2 to Co3 and the voltage difference $V=V^{+}-V^{-}$ is detected between Co3 and Co4. All measurements presented in this paper are taken in the nonlocal configuration.

Figure 2

Nonlocal spin valve measurement: the transresistance $V∕I$ as a function of the in-plane magnetic field for positive and negative sweep direction. (a) Device A, two switch traces of the cobalt electrodes and (b) Device B, four switch traces, at low temperature $\left(2\mathrm{K}\right)$.

Figure 3

(Top) Experimental data (dots) and fitting results (lines) using Eq. (1) for nonlocal spin valve at room temperature, device C. The letters $a$ to $d$ represent the different magnetic configurations as described below. (Bottom) Spatial dependence of ${\mu }_{\uparrow }$ and ${\mu }_{\downarrow }$ electrochemical potentials in the Al island for the magnetic configurations $a$ to $d$, as in the top panel. The filled (open) dots indicate the potential measured by the $V^{+}$ and $V^{-}$ probes.

Figure 4

Nonlocal spin accumulation at room temperature, device D. The fitting based on Eq. (1) returns ${\lambda }_{\mathrm{sf}}=(350\pm 50)\mathrm{nm}$ and a polarization of $P=(8\pm 1)\%$.