Electrical detection of the spin Hall effect in ferromagnet-semiconductor heterostructures.

摘要

This thesis describes the effects of spin-orbit coupling on electron transport in Fe/ InxGa1-xAs heterostructures. Spin-orbit coupling is a relativistic phenomenon that couples the spin of an electron to its momentum by means of a momentum-dependent effective magnetic field. The spin-orbit coupling in bulk InxGa 1-xAs is determined by measuring the direct spin Hall effect. In the direct spin Hall effect, an applied charge current induces a spin current due to spin-orbit coupling. The spin current flows in a direction that is perpendicular to the charge current, with a spin orientation that is perpendicular to the flow direction of both the charge current and the spin current. The spin Hall effect leads to an out-of-plane spin accumulation that is opposite in sign at opposite edges of the channel.;Lateral Fe/InxGa1-xAs devices are fabricated using standard semiconductor processing techniques. The interface between the Fe and InxGa 1-xAs is a highly doped Schottky tunnel barrier for efficient electrical spin injection and detection. Measurements of the spin valve and Hanle effect are performed in the non-local geometry to confirm that the Fe electrodes are sensitive to spin polarization in the InxGa 1-xAs channel and its dephasing by precession in an applied magnetic field. The spin accumulation due to the spin Hall effect is identified through the observation of a Hanle effect in the Hall voltage measured by pairs of ferromagnetic contacts at the channel edges. The data are fit using a model which includes spin diffusion, precession, and relaxation. We use the parameters determined from the fit to calculate the spin Hall conductivity. We find that the magnitude of the spin Hall conductivity is in agreement with models of the extrinsic SHE due to ionized impurity scattering. By analyzing the dependence of the spin Hall signal on channel conductivity we determine the contributions of both skew and side jump scattering to the total spin Hall conductivity. We calculate that the spin-orbit coupling parameter is larger than predicted by standard k ˙ p perturbation theory.