Spintronics promises smaller, more powerful microchips

Cobalt green, as it is known, has been tested by a US team who believe it could be used in "spintronic" devices.

Spintronics involves manipulating the magnetic properties of electrons to do useful computational work.

Cobalt green may be useful for building working devices as it can be used at room temperature, unlike many other materials which must be supercooled.

"The big challenge is to develop materials that can perform these kinds of functions not just at cryogenic temperatures but at practical temperatures," said Professor Daniel Gamelin of the University of Washington in Seattle, one of the team that carried out the work.

Magnetic force

Cobalt green, sometimes known as Rinmann's green, is a mixture of zinc oxide and cobalt. The semi-transparent pigment was developed by the Swedish chemist Sven Rinmann in 1780.

The colouring never found favour with artists as it was expensive and created relatively weak colours.

The breakthrough with the materials we tested is that they exhibit their magnetic properties at room temperature Professor Gamelin

However, the material could be useful in spintronic devices because of its magnetic properties.

Conventional electronics rely on the movement and accumulation of electrons to carry out calculations or to store data.

In addition, spintronics uses the spin of electrons - detected as a weak magnetic force - to increase the computational power of a device.

Spintronic devices, in theory, should be much quicker than conventional electronics and require much less power.

The technology is already used in some hard discs and could eventually be used for sensors and computer memory.

Antique promise

A goal of spintronics is to develop a semiconductor that can manipulate an electron's magnetism.

Semiconductors are used to manufacture microchips, at the heart of all computers and many other electronic devices.

Semiconductors are at the heart of all computers

As computers have become faster, chips have become smaller.

But manufacturers recognise that conventional chip fabrications techniques will eventually reach a physical limit.

Spintronics offers a potential solution.

To create a useful spintronic device the semiconductor must be magnetised and remain stable at room temperature.

Researchers have proposed that the best way to create material like this is to incorporate a magnetic element into a traditional semiconductor such as silicon.

Until now, most attempts to do this have only shown useful spintronic properties at low temperature, typically around minus 200C. This is much too cold to be useful in a working device.

Cobalt green appears to work at more useful temperatures.

"The breakthrough with the materials we tested is that they exhibit their magnetic properties at room temperature," said Professor Gamelin.

Chip makers

To test the antique pigment the researchers processed zinc oxide, a simple semiconductor material, so that some of the zinc ions were replaced with ions of magnetic cobalt. The process is known as "doping".

This work shows there is a real effect here, and there is promise for these materials Professor Gamelin

The cobalt ions were then aligned by exposing the semiconductor to a zinc metal vapour. The alignment causes the material to become magnetic.

The magnetism continued when the material was warmed to room temperature and when the exposure to the zinc metal vapour was stopped.

When the material was heated further the magnetic properties disappeared.

"This work shows there is a real effect here, and there is promise for these materials," said Professor Gamelin.

However, the research is still in its early stages. To be of use to chip-makers the technique must be shown to work using common semiconductor material.

"The next step is to try to get these materials to interface with silicon semiconductors."