2016-05 Computational discovery of a giant interface spin Hall effect

An electron is a charged particle that spins like a top. The spin Hall effect (SHE) refers to the generation of a current of "spins" at right angles to a current of charge in a suitable conductor; it results from a combination of disorder and a relativistic effect called the spin-orbit interaction. The SHE and its inverse allow pure currents of spin to be created, manipulated and detected electrically with huge potential for realizing better magnetic storage devices. The materials at the cutting edge of experimental studies are very complex involving bilayers of heavy, non-magnetic metals like platinum, and metallic magnetic alloys like permalloy (containing 20% Fe and 80% Ni). Because applications are driving fundamental research in this field, most experiments are carried out at room temperature. The resulting complexity poses a huge challenge to theory. In a paper Giant Room Temperature Interface Spin Hall and Inverse Spin Hall Effects published in Physical Review Letters, a relativistic quantum mechanical approach was used to computationally study the SHE and its inverse in a permalloy-platinum bilayer. The so-called first-principles scattering approach describes the interface between the two materials as well as the alloy disorder and temperature induced disorder realistically on an atomic scale. A SHE was found that, contrary to received wisdom, increases with increasing temperature. The calculations predict that the SHE in bilayers is dominated by an interface contribution.