Manipulation of spin states in a semiconductor by microscale magnets

We present the ability to manipulate spin states in a semiconductor on a sub-micrometre length scale via the magnetic fringe fields of microstructured magnets. Fe/Tb multilayers with remanent out-of-plane magnetization induce a remanent, vertical magnetization in an underlying diluted magnetic semiconductor (DMS), which in turn results in an efficient spin polarization of optically excited charge carriers via sp-d exchange interaction. By optically switching the magnetization of the ferromagnet, the DMS magnetization can be manipulated and the limits of a dynamical interaction between the spin states in the ferromagnet and the magnetic semiconductor are discussed. Moreover, magnetic ion spins of the DMS initially aligned along the sample surface are tipped by optically generated, spin polarized holes, which leads to a coherent spin precession around the total magnetic field. We show that the fringe field of in-plane magnetized Co wires can be utilized to locally modify the coherent dynamics of the semiconductor magnetization and demonstrate how the field inhomogeneity influences the coherent response of the Mn spin ensemble in the DMS.