Spatial imaging of magnetically patterned nuclear spins in GaAs

We exploit ferromagnetic imprinting to create complex laterally defined regions of nuclear spin polarization in lithographically patterned MnAs/GaAs epilayers grown by molecular beam epitaxy. A time-resolved Kerr rotation microscope with \ensuremath{\sim}1 \ensuremath{\mu}m spatial resolution uses electron spin precession to directly image the GaAs nuclear polarization. These measurements indicate that the polarization varies from a maximum under magnetic mesas to zero several microns from the mesa perimeter, resulting in large $(\ensuremath{\sim}{10}^{4}\mathrm{T}/\mathrm{m})$ effective field gradients. The results reveal a flexible scheme for lateral engineering of spin-dependent energy landscapes in the solid state.