OVERVIEW

Spintronics is a generic name for spin-based electronic devices, which use the spin degree of freedom instead of the charge for information processing. The interest in spintronic devices is motivated by the anticipated lower power consumption and higher degree of functionality than in electronic devices. In addition, spintronic devices that rely on semiconducting materials can incorporate novel functionalities and are more adaptable, since the spin-dependent properties are, in many cases, controlled through electric fields. However, viable spintronic devices require efficient injection of spin-polarized electrons into nonmagnetic materials, minimization of spin dephasing, ability of spin control during transport, and, finally, efficient spin detection. Although some of these requirements have been successfully demonstrated, spintronic devices still await an experimental confirmation of the predicted theoretical expectations.

Because spin polarization arises naturally in ferromagnetic (FM) materials, the first spin-based devices were all-metallic structures, which consisted of layers of magnetic and nonmagnetic materials that form magnetic tunnel junctions and display hysteresis and giant magnetoresistance (GMR). In the GMR effect, the resistance changes from a small to a large value when the magnetizations of the FM layers change from parallel to antiparallel. These devices function as GMR sensors, circuit isolators, read heads, or magnetoresistive memory cells used as nonvolatile magnetic random access memories, which store trillions of bits defined as magnetization directions established by an external magnetic field (see overviews in [1 5]). The devices based on magnetoresistance effects and on the manipulation of ensemble magnetizations imposed the field of magnetoelectronics. Modern spintronic devices, on the...