Enhanced spin injection and detection in spin valves with integrated tunnel barriers

We study the spin-dependent transport in lateral spin-valve devices with aluminum oxide tunnel barriers at the interfaces between NiFe electrodes and an interconnecting Al strip. Different total conductivities per cross-sectional area are achieved by varying the oxygen pressure, the oxidation time, and the thickness of the oxidized aluminum layer. The experimental data are consistent with our theoretical description including spin diffusion, spin relaxation, and tunnel barriers at the interfaces between electrodes and aluminum strip. With decreasing tunnel conductance the amplitude of the nonlocal spin-valve effect increases by two orders of magnitude up to saturation.