Unipolar spin transistors and magnetic bipolar transistors

Until recently the field of spintronics has focused on magnetic metals for conducting components[1]. Multilayer spintronic devices, such as giant magnetoresistive (GMR)[2] and magnetic tunnel junction (MTJ)[3] devices, have revolutionized magnetic sensor technology and hold promise for reprogrammable logic and nonvolatile memory applications. In these devices an electric current flows through two ferromagnetic regions, and the device function relies on a significant change in the resistance depending on whether the magnetizations of the two regions are oriented parallel or antiparallel to each other. The device performance improves as the spin polarization of the constituent material approaches 100%, and thus there are continuing efforts to find 100% spin-polarized conducting materials. Interest in magnetic semiconductors for semiconductor spintronics can be traced in part to their near- 100% spin polarization; the high spin polarization comes from the small Fermi energies of these materials compared to magnetic metals.