Experimental search for the electrical spin injection in a semiconductor

The electrical injection of spin-polarized electrons in a semiconductor can be achieved in principle by driving a current from a ferromagnetic metal, where current is known to be significantly spin polarized, into the semicon ductor via Ohmic conduction. For detection a second ferromagnet can be used as a drain. We studied submicron lateral spin valve junctions, based on hi gh-mobility ZnAs/AlSb two-dimensional electron gas, with Ni, Co, and permal loy as ferromagnetic electrodes. In the standard geometry it is very diffic ult to separate true spin injection from other effects. including local Hal l effect, anomalous magnetoresistance contribution from the ferromagnetic e lectrodes and weak localization/antilocalization corrections, which can clo sely mimic the signal expected from spin valve effect. The reduction in siz e, and the use of a multiterminal nonlocal geometry allowed us to reduce th e unwanted effects to a minimum. Despite all our efforts, we have not been able to observe spin injection. However, we find that this "negative" resul t in these systems is actually consistent with theoretical predictions for spin transport in diffusive systems.