Electric control of the spin Hall effect by intervalley transitions.

Controlling spin-related material properties by electronic means is a key step towards future spintronic technologies. The spin Hall effect (SHE) has become increasingly important for generating, detecting and using spin currents, but its strength--quantified in terms of the SHE angle--is ultimately fixed by the magnitude of the spin-orbit coupling (SOC) present for any given material system. However, if the electrons generating the SHE can be controlled by populating different areas (valleys) of the electronic structure with different SOC characteristic the SHE angle can be tuned directly within a single sample. Here we report the manipulation of the SHE in bulk GaAs at room temperature by means of an electrical intervalley transition induced in the conduction band. The spin Hall angle was determined by measuring an electromotive force driven by photoexcited spin-polarized electrons drifting through GaAs Hall bars. By controlling electron populations in different (Γ and L) valleys, we manipulated the angle from 0.0005 to 0.02. This change by a factor of 40 is unprecedented in GaAs and the highest value achieved is comparable to that of the heavy metal Pt.

Electrically tunable spin injector free from the impedance mismatch problem.

Injection of spin currents into solids is crucial for exploring spin physics and spintronics. There has been significant progress in recent years in spin injection into high-resistivity materials, for example, semiconductors and organic materials, which uses tunnel barriers to circumvent the impedance mismatch problem; the impedance mismatch between ferromagnetic metals and high-resistivity materials drastically limits the spin-injection efficiency. However, because of this problem, there is no route for spin injection into these materials through low-resistivity interfaces, that is, Ohmic contacts, even though this promises an easy and versatile pathway for spin injection without the need for growing high-quality tunnel barriers. Here we show experimental evidence that spin pumping enables spin injection free from this condition; room-temperature spin injection into GaAs from Ni(81)Fe(19) through an Ohmic contact is demonstrated through dynamical spin exchange. Furthermore, we demonstrate that this exchange can be controlled electrically by applying a bias voltage across a Ni(81)Fe(19)/GaAs interface, enabling electric tuning of the spin-pumping efficiency.

Rewritable remote encoding and decoding of miniature multi-bit magnetic tags for high-throughput biological analysis.

We have investigated a new magnetic labelling technology for high-throughput biomolecular identification and DNA sequencing. Planar multi-bit magnetic tags comprising a magnetic barcode formed by an ensemble of micron-sized thin film ferromagnetic Co bars and a 15 x 15 micron Au square for immobilization of probe molecules have been designed and fabricated. We show that by using a globally applied magnetic field and magneto-optical Kerr microscopy the magnetic elements in the multi-bit magnetic tags can be addressed individually and encoded/decoded remotely. The power of the approach is the read/write technique, which allows modest globally applied magnetic fields to write almost unlimited numbers of codes to populations of tags rather than individuals. The magnetic nature of the technology also lends itself naturally to fast, remote decoding and the ability to rewrite tags if needed. We demonstrate the critical steps needed to show the feasibility of this technology, including fabrication, remote writing and reading, and successful functionalization of the tags as verified by fluorescence detection. This approach is ideal for encoding information on tags in microfluidic flow or suspension, in order to label oligonucleotides during split-and-mix synthesis, and for combinatorial library-based high-throughput multiplexed bioassays.