Enhancement of spin injection from ferromagnetic metal into a two-dimensional electron gas using a tunnel barrier - art. no. 161307

Using free electron approximation, we calculated the spin dependent tunnel conductance of ballistic ferromagnet/tunnel barrier/two-dimensional electro n gas (FM/I/2DEG) junctions and FM/I/2DEG/I/FM double junctions for differe nt barrier strengths. We find that a tunnel barrier improves spin injection considerably. For sufficiently strong barriers, it is predicted that the t unnel conductance ratio between spin up and spin down channels is, in first approximation, equal to the ratio between their Fermi velocities in the FM . For single junctions, this results in a significant current polarization (similar to 10%). This corresponds to a relative resistance change of sever al percent between parallel and antiparallel magnetization of the two FM el ectrodes, respectively, for the double junction. In the weak barrier regime , the magnitude and sign of the current polarization are strongly dependent on the (controllable) electron density in the 2DEG.