A development that could advance of the hottest areas of physics research - "spintronics" - has been announced by US scientists.

Ultimately, physicists hope that research in spintronics could lead to smaller, faster and less power hungry computers. These machines would operate using logic devices based on manipulating and measuring the spin of electrons, rather than turning current on and off.

Now researchers have for the first time shown that they can inject spin-polarized electrons into silicon, manipulate them, and measure them coming out the other side.

This is important because spintronic components built from silicon could be made using existing manufacturing technology. Until now, however, it has proven difficult to inject and measure spin in silicon.

using silicon has been difficult because it causes passing electrons to lose their spin state.

Spin is a quantum property of electrons closely related to magnetism, and individual electrons have a spin that is either "up" or "down". In a typical electric current, electrons have both kinds of spin, but passing the current through a ferromagnet filters them out.

Spin doctoring

Electrons with spin oriented opposite to the axis of the magnet will be slowed and scattered, while electrons with spin oriented along the magnetic axis will be drawn through. This creates a polarised current consisting of electrons with more of one direction of spin than the other.

The spin of these electrons can then be identified by passing the current through another magnet.

Previously, researchers have made spintronics work with metals, and with semiconductors like gallium arsenide. But silicon has proven a frustrating material to work with. A major problem is that when you bond ferromagnets to silicon, materials called silicides are formed and these scramble a spin-coherent current.

Now, though, Ian Appelbaum and Biqin Huang of the University of Delaware in Newark, US, and Douwe Monsma of Cambridge NanoTech, Massachusetts, US, have shown that spin can be injected and detected using a silicon-based device.

Keeping cool

The researchers passed highly energetic electrons through thin-film ferromagnets 5 nanometres in depth, which were deposited on top of a 10-micron-thin wafer of silicon. The entire set-up was cooled to 85K (-188C).

Keeping the layers very thin and using high-energy electrons allowed electrons to move through the silicon without losing their spin. This made it possible to inject current with a particular spin state into the silicon, and measure it at the other end.

The team also showed that they could change the spin of the electrons within the silicon by subjecting them to a magnetic field.

"This is a very important demonstration," says David D. Awschalom, a physicist at the University of California in Santa Barbara, US. "It's an important step for the community."

Igor Zutic, a physicist at the University at Buffalo, State University of New York, US, adds that the next step will be to show that the devices can work at higher temperatures and using off-the-shelf silicon that is not entirely pure.