Japanese scientists have developed a transistor that could be a step towards a ‘spintronic’ computer, which would process data encoded in the spin, or magnetic orientation, of electrons.

Transistors are the fundamental building blocks of computers. They allow a small electric current to switch a larger current on or off, and assemblies of transistors are the basis of the logic gates inside every microprocessor. These gates process data in the form of electric current, but this has two key drawbacks: data is lost when the power is switched off, and transistors cannot be made much smaller than their present size, with features measuring in the tens of nanometers.

One alternative approach is spintronics — computing based on electron spins. Spintronic devices could be much smaller than conventional computer chips, and spin states do not need to be sustained by a power source, so the data they carry is non-volatile. But none of the spin transistors proposed to date have been able to achieve substantial power amplification, or ‘gain’, at room temperature. Yoshishige Suzuki and colleagues at Osaka University and the National Institute of Advanced Industrial Science and Technology in Tsukuba1 have now developed a device that does just that.

Fig. 1: The spin transistor could one day form the basis of smaller computer chips.

The group's ‘spin transistor’ relies on a magnetic tunnel junction: an insulating layer of magnesium oxide just a nanometer wide sandwiched between two slightly thicker layers of a ferromagnetic iron-cobalt mixture. If those two layers are magnetized in the same direction, electrons with matching spin can tunnel across the insulating barrier, producing a current.

The scientists used an external wire to generate a magnetic field to sense when current flowed through the junction. This current then controlled the switching of a second junction. Although the current declined from junction to junction, the power gain of the device was 5.6, the first time that the output of a spin transistor at room temperature has been greater than its input. The scientists say that it should theoretically be possible to reduce the resistance of the system to produce a substantially higher current gain, potentially making their technology the basis of a spin logic device.