Scanning Kerr Rotation Microscopy of Lateral Spin Transport Devices

Scanning Kerr-rotation microscopy is employed to image electrical spin injection and accumulation in the GaAs channel of lateral spin transport devices having ferromagnetic Fe/GaAs Schottky barrier source and drain contacts [1]. Because electrically-injected spins are initially oriented in the $xy$ sample plane ($S_0 \parallel \hat{x}$), we measure the Kerr rotation ($\theta_K \propto S_z$) as a function of small in- plane magnetic field ($B_y$). We specifically investigate how these ``Hanle curves" vary across a series of devices with systematically increasing electron density $n_{e}$ in the n-type GaAs channel ($2\times10^{16}$ cm$^{-3} < n_{e} < 3\times10^{17} $ cm$^{-3}$). The width of the Hanle curves near the source contact increases with $n_{e}$, reflecting the decreasing electron spin lifetime. The amplitude of the Hanle curves (a measure of the spin polarization) decays on a lengthscale related to the $n_{e}$-dependent spin diffusion constant, lifetime, and mobility. [1] S.A. Crooker, M. Furis, X. Lou, C. Adelmann, D.L. Smith, C.J. Palmstr$\o$m, P.A. Crowell, Science \textbf{309}, 2191 (2005).