Large spin Hall effect measured at room temperature
RIKEN scientists have accurately measured a tiny voltage produced by segregating electrons according to their spin (1), a result which could help to usher in a new era of spin-based computing.
Conventional computers process and communicate information by shunting electrons around, but store data in the magnetic properties of tiny segments of a spinning disk drive. Yet that magnetism is also due to electrons—as each charged particle spins, it creates a magnetic moment. Electrons can spin ‘up’ or ‘down’, creating opposing poles like a bar magnet, and the burgeoning technology of spintronics uses these two states to represent bits of binary data. As well as storing information, these states can potentially be used to perform calculations.
The spin Hall effect (SHE) provides an important way to control these spinning electrons. The Hall effect itself (identified in 1879 by Edwin Hall) occurs when a magnetic field forces a current of electrons flowing through a flat plate to veer to one side. This causes charge to accumulate on that side of the plate, setting up a voltage across it. In a similar way, the SHE sends spin-up electrons to one side of the plate and spin-down to the other, setting up a ‘spin current’ (Fig. 1 - Click on link below).
Spin current is an important factor in operating future spintronic devices. Ferromagnets are normally used to differentiate spins, but interference between neighboring magnets makes it tricky to build working spintronic devices that way.
“However, if we use SHE, we can generate the spin current without using a ferromagnet,” says Takashi Kimura of RIKEN’s Frontier Research System, Wako. This could allow much easier integration of semiconductor and spintronic devices in the future.
Kimura and the team leader YoshiChika Otani have now found that the spin Hall conductivity—the potential for electrons to migrate due to the SHE—in a platinum wire is a thousand times greater than in previous experiments with semiconductor materials, making it easier to study and exploit the effect. Their electrical measurement technique is also more precise than the optical detection method usually employed.
It’s significant that the team has detected this effect at room temperature. It means that SHE is not only a physically interesting phenomenon, but also a useful way of manipulating spins in future spintronic devices, says Kimura.
The team is now trying to identify materials that produce even greater SHE conductivities. “We hope that new devices using SHE are proposed in near future,” says Kimura.
Reference
1. Kimura, T., Otani, Y., Sato, T., Takahashi, S. & Maekawa, S. Room-temperature reversible spin Hall effect. Physical Review Letters 98, 156601 (2007).
