Spin transfer experiments on (Ga,Mn)As/(In,Ga)As/(Ga,Mn)As tunnel junctions

We present and discuss the results of current induced magnetic switching experiments performed on pillar-shaped (Ga,Mn)As/(In,Ga)As/(Ga,Mn)As tunnel junctions. The sign of the switching currents confirms the opposite spin polarizations of the valence band holes and Mn atoms in (Ga,Mn)As. With respect to spin transfer experiments in purely metallic structures, the magnitude of the switching currents is smaller by two orders of magnitude, which can be explained mainly by the small magnetization of (Ga,Mn)As. A striking result is the observation of current induced magnetization switching at values of the bias voltage for which the magnetoresistance of the junction has dropped to almost zero. This raises interesting questions on the different role played by voltage-induced magnon excitations on magnetoresistance and current-induced magnetization switching.