Spin doctors

Imagine you switch on your PC, and it's instantly ready to go - there's no tedious boot-up sequence to sit through.

You don't have to worry about your hard disk coming up to speed, because you don't have one. Instead, you have gigabytes of very cheap and very fast RAM that even remembers its data when powered off.

And you have a CPU that can be dynamically reprogrammed to provide optimum instruction sets for particular applications.

That's quite a wish list, but it may become the norm in just a few years' time.

So, how will it come about? It's all about spinning electrons. Conventional electronics treat electrons as blobs of electric charge. But electrons have another property, known as "spin".

Now, an emerging field called "spintronics" is promising a whole range of electronic devices in which an electron's spin is as important as its charge.

Imagining electrons

It's hard to stop yourself imagining electrons as tiny solid spheres, orbiting an atom and tumbling down wires to make an electric current.

In this picture, the idea that electrons spin seems plausible. But electrons aren't really solid spheres - their "reality" can only be properly described by the equations of quantum mechanics.

It's impossible for us to visualise what they are really like because the quantum world is so strangely different from our large-scale world.

While an electron's spin may not be a real twirly spin in the sense we normally understand, it's still a measurable property of the electron and, like everything in the quantum world, can take only a few distinct values.

All electrons have the same amount of spin; it's only the direction that can be different, and there are only two possibilities: up and down.

The obvious exploitation of electron spin is to use the two different spins to represent a zero and a one respectively. It's an intriguing thought that a current of electricity can also encode binary data, but this technology is already a reality: in 1997, IBM first demonstrated the use of spintronics in a hard-disk read head, allowing vastly improved data density and access speed.

Spintronics sandwich

One of the basic spintronics devices is the spin valve. It's a sandwich with two tiny plates of magnetic metal enclosing a filling of non-magnetic metal. If a current of electrons is fed into the top plate, only those electrons whose spins are aligned with the electron spins in the magnetic metal will pass through the non-magnetic layer to the lower magnetic plate.

Electrons whose spins do not match are blocked. Because the spins of the electrons can be easily changed (using a magnetic field) in the magnetic layers, the device can be configured to allow only spin-up or spin-down electrons to pass through.

The spin valve can also serve as a memory cell, storing, say, a one if the spin orientations on both plates are the same, and a zero otherwise.

Magnetic RAM

Since this is a property at the atomic level, it persists when the device is switched off. Such magnetic RAM, or MRAM, has already been demonstrated in the laboratory, and the race is on to bring it to market.

In future PCs, the entire operating system, and all your favourite applications, may be preloaded in MRAM, allowing your machine to spring into life immediately on power-up. And using spintronics devices as logic gates might allow the construction of CPUs whose architectures are dynamically reconfigurable.

Once the technology moves from the research laboratory to the marketplace, watch out. Since the conventional silicon-chip manufacturing processes can easily be adapted to the production of spintronics systems, we may soon be witnessing the beginning of a massive change in computing technology.