Magnetic field-induced full rotation of collective spins flowing in a non-magnetic metal A route toward development of spin-based low power logic devices

Digital information is generally stored by as spin direction in a ferromagnet. This spin information can be injected into a non-magnetic metal such as silver and converted to spin accumulation or to pure spin-current for transferring information or logic operations. Such spin accumulation devices are expected to be employed in the development of low-noise read-head sensors for next-generation hard disk drives. However, because of low spin injection efficiency, it has been difficult not only to control spin direction using external fields but also to clarify spin transport properties.

Spins are injected into nonmagnetic Ag by applying a bias current across the FeNi/MgO/Ag interface
© Yoshichika Otani
After the injection, the spins diffuse along the Ag nanowire. The efficiency of pure spin current generation in lateral spin valves is improved by increasing the interface for the spin injection and confining the spin current solely to the detector. The application of the perpendicular magnetic field exerts torque on spins, inducing their precession.

Professor Yoshichika Otani (University of Tokyo Institute for Solid State Physics and RIKEN Quantum Nanoscale Magnetics Team leader), Associate Professor Yasuhiro Fukuma (Frontier Research Academy for Young Researchers, Kyushu Institute of Technology), and graduate student Hiroshi Idzuchi (Graduate School of Advanced Materials) have developed a method to enhance the spin injection efficiency by a factor of 3.2 compared with that of a conventional device with a single injector junction. The researchers succeeded in observing long distance transport of pure spin current over 10 ?m and also manipulating the direction of the injected spin by applying external magnetic fields. Theoretical analyses revealed that the difference in spin travelling time over the travelling distance reduced as distance increased, and therefore the spins flowing in a silver wire can complete a full rotation. Moreover they found that this tendency is a universal behavior as a function of the normalized separation between the injector and the detector in a material-independent fashion for metals.

This technique will help in designing pure spin current circuitry and, once the technology to control spin with electric fields is established, may lead to the development of high speed spin-based logic circuits which exceed existing semiconductor technologies.

Paper

Hiroshi Idzuchi, Yasuhiro Fukuma, YoshiChika Otani,
“Towards coherent spin precession in pure-spin current”,
Scientific Reports Online Edition: 2012/09/04 (Japan time), doi: 10.1038/srep00628.
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