Spin polarized tunneling at finite bias

We fabricated mesoscopic lateral-spin-valves [1] with spin transresistances as high as 2.5 Ohm. We employed these devices to measure the bias dependence of the polarization of the electrons tunneling \emph{from} and \emph{into} a ferromagnet. Our measurements show an intrinsic asymmetry between these two processes. Using a free-electron model, we found that the polarization is strongly suppressed for electrons tunneling \emph {into} the ferromagnet due to the reduced polarization for hot electron states and a spin-dependent wave-vector matching effect through the tunnel barrier. [1] M. Johnson and R. H. Silsbee, Phys. Rev. Lett. {\bf 55}, 1790 (1985); F.J. Jedema et al., Nature {\bf 416}, 713 (2002).