Chapter 1

Spin-dependent effects attract a great attention since 1922 when the German physicists Otto Stern and Walther Gerlach performed an experiment that confirmed that atoms have an intrinsic angular momentum, whose projection on a chosen axis is quantized. [40]. Thereafter the spin hypothesis was introduced in 1925 by Samuel Goudsmit and George Uhlenbeck. The spin concept had been accepted since it helped to describe thin spectral lines in Zeeman spectra [126]. During the following couple of decades the concept of spin had been used by Werner Heisenberg to explain ferromagnetism [18], then Wolfgang Pauli introduced particle statistics (fermions – particles that obey Fermi-Dirac statistics and are characterized by half-integer spin, and bosons – particles that obey Bose-Einstein statistics and are characterized by integer spin) [127], and nuclear magnetic resonance (NMR) spectroscopy was invented. Since the 1950s magnetic effects are widely used to store data. The first devices were quite large and were only able to store several tens of kilobytes of data. Advances in technologies made it possible to increase the storage data density significantly [120].

In 1971 Mikhail D’yakonov and Vladimir Perel’ predicted a spin Hall effect - a spin flow in the direction perpendicular to the current [25]. The first experimental confirmation of the prediction has been made by Vorob’ev [119]. Vorob’ev et al. observed a change in the rotation rate of the plane of the polarization of light propagated in a Te crystal. The same effect was demonstrated by Yuichiro Kato in 2004 [63]. Kato used GaAs to demonstrate electrically induced electron-spin polarization near the edges of a semiconductor channel. In 1976 Arkady Aronov and Gregory Pikus proposed an idea that spin-polarized current can be injected into a semiconductor when a current is passed through a ferromagnet/semiconductor junction [6]. Santos F. Alvarado and Philippe Renaud in 1992 observed the experimental evidence for the tunneling of polarized electrons from the apex of a ferromagnetic Ni tip into GaAs(110) [4].

The most impressive result of spin electronics is the giant magnetoresistant (GMR) effect used in hard drives and magnetic random access memory. The giant magnetoresistance is the quantum-mechanical effect observed in thin ferromagnetic films that are connected by a thin metallic film. The effect causes a considerable change of resistance in such structure if the orientation of ferromagnetic layers changes from parallel to antiparallel. This effect is based on the scattering of electrons depending on their spin orientation relative to the magnetization direction. The direction of the magnetization of the ferromagnetic layer can be controlled by an external magnetic field. The Physics Nobel Prize in 2007 was given to Peter Grimberg and Albert Fert for the discovery of the giant magnetoresistance [3]. The resistance change between spin parallel and spin antiparallel arrangements can also be observed in magnetic tunnel junctions. Studies on the tunneling magnetoresistance (TMR) effect have been advanced recently resulting further improvement of recording heads was achieved by using TMR [10513293].

The last decades success in digital electronics has been provided by the advances in silicon chip developments and its core idea that the information in microelectronic devices can be stored and manipulated by controlling the electron charge. According to the well-known Moore’s law the number of transistors on a chip doubles approximately every two years [7978]. However, the International Technology Roadmap for Semiconductors (ITRS) in 2010 predicted that the trend will slow down to a three-year cycle [1]. The increase of the number of transistors leads to an increase of the power consumption and speed of the chip. Since 1965 when this trend was described by Gordon E. Moore the progress has followed this exponential trend. This trend in silicon–based computing will come to an end in the next decades. When the capabilities of miniaturization become limited by an atom size. The size reduction leads to large leakages currents that can be reduced by strain techniques, the use of high-K dielectric materials, and tri-gate FET. The classic scaling ended at 130nm [66] but these new boosters keep the trend up. Although an atomic size is an ultimate limit. The real stopper of scaling happen earlier due to high costs and is likely to economical-based motivation [9899].

In 1990 a device that does not use charge to process information but spin orientation was proposed by Supriyo Datta and Biswajit Das. This device is commonly called Datta-Das transistor or spin field-effect transistor (SpinFET). The potential advantages of such a device are to go beyond conventional silicon-based transistors. The physical principles behind the SpinFET are similar as for the tunneling magnetoresistance effect.

Electrical and optical spin manipulation is possible due to spin-orbit coupling, that makes the spin degree of freedom respond to its orbital environment [125]. In semiconductor nanostructures the strength of the spin-orbit coupling depends on the symmetry of the system, its geometric and energy parameters, which can vary over a wide range of values [125]. Current research is governed by the fact that utilizing spin properties of electrons for future microelectronic devices opens great opportunities to reduce the device power consumption. In recent years spintronic devices, where the spin of the electron is used as an additional degree of freedom to tune their properties, have received much attention [13631128].