Tunneling Magnetoresistance and Scanning Tunneling Microscopy with Polarized Electrons

The controlled injection of spin-polarized charge carriers from a ferromagnetic material into a semiconductor has lately become one of the most important topics in solid-state physics because of the potential advantages of controlling the electron spin in electronic switching devices. Prerequisites for the realization of spintronic devices are (1) The efficient injection of highly polarized electrons at a ferromagnetic-semiconductor interface, and (2) the spin-sensitive detection of the injected electrons. Since the first report in 1975 of spin-dependent transport in a tunnel junction composed of two ferromagnetic layers separated by an insulating barrier, the field of spintronics has made considerable experimental and theoretical progress. A major challenge in the research field of spintronics is the achievement of polarized-electron injection at the junction formed between a ferromagnetic metal (FM) and a semiconducting (SC) material. So far the achieved degree polarization of the electrons injected at a metal/semiconductor junction has been modest. However, tunneling experiments, in which electrons are injected through a vacuum barrier from the ferromagnetic metal into a semiconductor show that a spin polarization much higher than hitherto demonstrated should be achievable in a FM/SC junction.