Exploring spin-transfer and spin-Hall effects in mesoscopic metallic structures

Yi Ji

University of Delaware

Spintronics relies on the functionalities of spin currents. The concept of a pure spin current holds a unique place in spintronics. One can visualize a pure spin current by considering electrons with opposite spins flow in opposite directions. Pure spin currents are less invasive and less dissipative compared to spin polarized charge currents. A pure spin current can be generated by electrical injection from a ferromagnet in a mesoscopic lateral structure known as nonlocal spin valve (NLSV). With low-resistance oxide injection interfaces and high quality nonmagnetic channels, the pure spin current can be large enough to induce magnetization reversal for a nanoscale magnet through the spin transfer effects.
A different approach to generate a pure spin current without a ferromagnet has been recently discovered and known as the spin-Hall effects. When electron currents flow in a heavy nonmagnetic metal such as platinum (Pt), the spin-orbit coupling causes electrons with opposite spins to be scattered into opposite transverse directions. Therefore a pure spin current is generated in the direction that is transverse to the electron current. We have fabricated mesoscopic structures in which a Pt wire is in contact with a Cu channel and an AlOx barrier is placed in between. The pure spin current due to the spin-Hall effect in Pt is injected into the Cu channel across the AlOx barrier. The injected spin accumulation in Cu is comparable to that from an electric spin injection using a ferromagnet, demonstrating the effectiveness of spin-Hall effect as a novel way to generate spin currents.
This work was supported by US DOE grant No. DE-FG02-07ER46374.