Spin Control of Drifting Electrons using Local Nuclear Polarization in Ferromagnet-Semiconductor Heterostructures*

We demonstrate a spatially-confined magnetic field gate to modulate the Larmor frequency of an optically-injected spin ensemble drifting down a GaAs channel [1]. The gate is activated either optically or electrically and polarizes GaAs nuclear spins at the interface between a lithographically-defined MnAs island and the channel via the ferromagnetic proximity polarization effect. We measure the rotation angle of the spin ensemble as it emerges from the polarized region using time-resolved Kerr rotation. The ensemble's spin rotation angle can be tuned by up to 5$\pi$ radians as the spins travel over 30 $\mu $m by controlling the nuclear field strength and adjusting the drift velocity. \\[4pt] [1] M.E. Nowakowski, et. al., Phys. Rev. Lett. 105, 137206 (2010)