Electron and Spin Transport

Abstract

In this chapter we shall take a look at electron and spin transport across interfaces. In the first major section we discuss fundamental spin-dependent phenomena that occur during current flow from a ferromagnet to a non-magnet and vice versa. We shall see that such flow leads to the build-up of a spin-dependent interface voltage which will be shown to directly lead to the important phenomenon of giant magneto-resistance. In the second major section we discuss the injection of spin polarized currents into a ferromagnet, so-called spin injection. In particular, we discuss the use of spin injection to directly switch the magnetization in a nanoscale magnetic structure. This interesting phenomenon, which is based on the use of the short-range and strong exchange interaction to provide the energy and torque for switching, differs from the conventional switching method which uses long-range Oersted fields produced by current carrying wires or coils. In the final two sections we touch on spin-dependent phenomena in semiconductors and consider the requirements for building a spin current amplifier, whose invention would revolutionize the whole field of spin dependent phenomena. 14.1 Currents Across Interfaces Between a Ferromagnet and a Nonmagnet In this section we consider the case of an electron current flowing across an interface between a ferromagnet and a non-magnet. We assume that the current is steady, i.e., that it does not depend on time, and derive basic consequences which arise from the fact that such a current is necessarily spin polarized.