New concepts for the Spin Hall Effect and its exploitation in spintronics – SPINHALL

Spintronics is based on the manipulation of spin-polarized currents and, in classical spintronics, the “spin currents” are generated or detected by ferromagnetic materials. An alternative that is foreseen today is based on the exploitation of the Spin Hall Effect (SHE) for spintronics without ferromagnetic materials. The SHE of a nonmagnetic conductor is due to the deflection of the spin up and spin down electrons in opposite directions by spin-orbit (SO) interactions. In a nonmagnetic conductor, these deflections generate spin accumulations, without charge accumulation, on the edges of the conductor. This spin accumulation can be used to produce (or detect) pure spin currents.
The SHE is characterized by its Hall angle phi_H which is the ratio between non-diagonal and diagonal elements of the conductivity tensor for a given spin. The possible yield for the conversion from charge current density into spin current density is given by phi_H. The SHE has been essentially studied for pure materials and, up to 2008, phi_H did not exceed 3x10-3 (the value for Pt), a too small value to compete with the production of spin currents in ferromagnets. In 2008 a surprising value of 11% (phi_H = 0.11) was found for gold and ascribed to iron impurities. Even larger effects (15%) were then obtained with gold doped with 3% of Pt. This took out of memory results obtained in 1981 by one of the partners of the project (AF) with values of phi_H up to 5% for Cu doped with Ir, Lu or Ta, large values already ascribed to resonant skew scattering on 5d levels split by SO. These results show a possible way for large yields, i.e. resonant scattering on localized levels split by SO. Our project includes:
1) the fabrication of nanostructures for lateral spin transport and SHE measurements, the first in France; 2) SHE measurements on various systems in which resonant scattering on localized levels split by SO is expected; 3) developments of models not only for the skew scattering but also the side jump SHE.; 4) the analysis of the advantages of SHE and their demonstration in spin transfer devices to switch a magnetic dot or generate microwave oscillations.