Designers of next-generation electronics are trying to take advantage of both the electron’s charge and spin. The success of spintronic devices therefore hinges on the ability to convert between spin and charge currents. The direct spin Hall effect is typically used to probe spin-orbit coupling in these materials, but the technique cannot be applied to semiconductors with long spin lifetimes, such as indirect bandgap silicon. Researchers Kazuya Ando and Eiji Saitoh at Tohoku University in Sendai, Japan, have turned their attention to the inverse spin Hall effect (ISHE), which makes use of the high resistivity of semiconductors to detect tiny spin currents. Ando and Saitoh show that it is possible to study spin-orbit interactions using ISHE in otherwise unmeasurable systems.
As reported in the January 17 issue of the online journal Nature Communications (DOI: 10.1038/ncomms1640), the researchers first deposited a thin-film heterostructure of Ni81Fe19/B-doped Si onto a silicon-on-insulator substrate and laid down ohmic AuPd contacts to detect the in-plane Hall voltage. They then measured the voltage across the AuPd contacts with a magnetic field applied at 0° and 180° normal to the plane of the sample. They found that the Hall voltage depends on the direction of the magnetic field around the ferromagnetic resonance edge, which is indicative of the ISHE effect.
The researchers next meas-ured the voltage dependence on the angle of the out-of-plane magnetic field. This revealed that a spin current is injected into the Si layer and that it precesses around an axis parallel to the applied magnetic field (see figure). Using the Landau–Lifshitz–Gilbert equation, Ando and Saitoh were able to demonstrate dynamical spin injection in p-type silicon at room temperature and unambiguously extract the ISHE contribution from the silicon layer. This technique can be used to explore the spin Hall effect in silicon with different dopants and doping levels, according to the researchers.
Moreover, the researchers said that their technique can be applied to understand other materials with weak spin-orbit interactions. This makes it particularly useful for spin-current detection in semiconducting systems and opens many new areas for spintronics research.
(a) Schematic of the Ni81Fe19/Si sample in spintronics study; (b) the precession of spins in the silicon layer measured by the inverse spin Hall effect (ISHE). H is applied oblique to the film plane; M denotes the static component of the magnetization; θ and ϕ show the magnetic field angle and magnetization angle, respectively; and js is the spin current. Reproduced with permission from Nat. Commun., DOI: 10.1038/ ncomms1640. © 2012 Macmillan Publishers Ltd.
