  We demonstrate the spin valve effect by ballistic transport in fully
epitaxial MnAs ferromagnetic metal / GaAs semiconductor / GaAs:MnAs granular
hybrid heterostructures. The GaAs:MnAs material contains ferromagnetic MnAs
nanoparticles in a GaAs matrix, and acts as a spin injector and a spin
detector. Although the barrier height of the GaAs/MnAs interface was found to
be very small, relatively large magnetoresistance was observed. This result
shows that by using ballistic transport, we can realize a large spin valve
effect without inserting a high tunnel barrier at the ferromagnetic metal /
semiconductor interface.
