Connecting the worlds of semiconductors and magnets: Researchers from the Institute of Physics ASCR realize an efficient spin-charge converter

Current information technologies are either charge-based or spin-based. Semiconductor microprocessors are prime examples among the large variety of charge-based devices. They utilize the possibility offered by semiconductors to easily electrically manipulate and detect their electronic charge states representing the zeros and ones. Spin-based devices operate on an entirely distinct principle. In some materials, like iron, electron spins spontaneously align their direction which generates magnetism. The position of the north and the south pole of the magnet can be used to represent the zeros and ones. This technology is behind memory applications such as computer hard disks. Efficient spin-charge and charge-spin convertors are needed for future technologies allowing to integrate the so far isolated worlds of semiconductor and magnetic devices.

Researchers from the Institute of Physics of the Academy of Sciences in Prague, in collaboration with researchers from the UK, Germany, and Japan, have discovered and efficient spin-charge converter in a common semiconductor material GaAs. The work has been published in the journal Nature Materials on August 10th, 2014 (DOI: 10.1038/nmat4059).

Figure: Electrons with their spin magnetic moments are deflected to the right or to the left depending on their spin direction due to the spin Hall effect. By this magnetization of electrons with a preferred spin orientation can be converted into electrical voltage. In a common semiconductor GaAs, this conversion is particularly efficient in one conduction valley (so called L-valley).

The device functionality is based on the relativistic phenomenon called the spin Hall effect which the Czech-UK group discovered in 2004 and which since then has become a text-book tool for converting electrical to magnetic signals, and vice versa, in a broad class of metals and semiconductors. So far, the most efficient spin-charge converters have been identified among heavy-metal elements such as platinum. Researchers from the Institute of Physics with their international colleagues found that one of the most common semiconductors GaAs can be turned into an as efficient spin Hall effect spin-charge converter as platinum. They utilized the property of semiconductors in which electrons can carry the current of their charge and spin in different conduction “valleys”. Researchers discovered that by moving carriers in GaAs from one to another valley, the spin-charge conversion efficiency increases in this semiconductor forty-times.

For detail information contact Tomas Jungwirth from the Institute of Physics ASCR,
Cukrovarnická 10, 162 53 Praha 6, e-mail: jungwfzu [dot] cz