We present and discuss the results of current induced magnetic switching experiments performed on pillarshaped ͑Ga, Mn͒As/ ͑In, Ga͒As/ ͑Ga, Mn͒As tunnel junctions. The sign of the switching currents confirms the opposite spin polarizations of the valence band holes and Mn atoms in ͑Ga,Mn͒As. 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,Mn͒As. 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.The magnetic moment of a ferromagnetic body can be reversed or reoriented by transfer of spin angular momentum from the electrons of a spin-polarized current. This spin transfer concept has been introduced by Slonczewski 1 and Berger, 2 and has been confirmed by extensive recent experiments on pillar-shaped magnetic trilayers ͑for a review, see Stiles and Miltat͒. 3 Most experiments 4-9 have been performed on purely metallic trilayers, for example Co/ Cu/ Co, with detection of the magnetic switching by giant magnetoresistance ͑GMR͒. A few experiments have been performed on magnetic tunnel junctions ͑MTJ͒, generally on standard junctions with metallic magnetic electrodes, 10-12 and recently on ͑Ga, Mn͒As/ GaAs/ ͑GaMn͒As junctions by Chiba et al. 13 Current induced magnetization switching ͑CIMS͒ experiments on tunnel junctions bring new physical problems, 14 and are of particular interest for their promising application to the switching of the MTJ of magnetic random access memory ͑MRAM͒. However, with standard MTJ made of magnetic metal electrodes separated by an insulating material, such as alumina, the combination of large tunnel resistances with high switching current densities ͑ϳ10 7 A cm −2 ͒ is a difficult obstacle for applications. In contrast, the low current density, of the order of 10 5 A cm −2 , needed for CIMS with ͑Ga,Mn͒As, 13 shows the interest of magnetic semiconductors for spin transfer. In this paper, we present results of CIMS experiments on pillar-shaped ͑Ga, Mn͒As/ ͑In, Ga͒As/ ͑Ga, Mn͒As tunnel junctions. ͑In-,Ga͒As has a smaller gap than GaAs and its choice for the insulating barrier allows us to obtain slightly smaller tunnel resistances than with GaAs. The offset of the valence band of ͑Ga,Mn͒As above that of GaAs is estimated to 100 meV. 15 A smaller value and therefore a lower barrier is expected when GaAs is replaced by ͑In,Ga͒As and as we will see, a tunneling behavior is still observed. After reporting on the experimental results, we will focus on the interpretation of the sign and amplitude ͑ϳ10 5 A cm −2 ͒ of the switching currents and we will also discuss our observation of CIMS effects in a voltage range where the magnetoresistanc...

We report on experiments and theory of resonant tunneling anisotropic magnetoresistance (TAMR) in AlAs/GaAs/AlAs quantum wells (QW) contacted by a (Ga,Mn)As ferromagnetic electrode. Such resonance effects manifest themselves by bias-dependent oscillations of the TAMR signal correlated to the successive positions of heavy (HH) and light (LH) quantized hole energy levels in GaAs QW. We have modeled the experimental data by calculating the spin-dependent resonant tunneling transmission in the frame of the 6 x 6 valence-band k.p theory. The calculations emphasize the opposite contributions of the (Ga,Mn)As HH and LH subbands near the Gamma point, unraveling the anatomy of the diluted magnetic semiconductor valence band.