May 10 2009
This week New Scientist cover article by journalist Eugenie Samuel Reich describes how a special material called spin ice, co-discovered in 1997 by Professor Steven Bramwell of the London Centre for Nanotechnology has come close to revealing a secret of the universe.
A magnet has two poles - north and south - but cut a magnet in half and each half has its own north and south pole. However much you divide a magnet, you can never isolate a pole on its own. You can't say carry a north pole in your pocket and leave the south pole at home. Yet if such isolated poles or "monopoles" were to exist they would explain a lot about the universe, as first realised by the Paul Dirac, the pioneer of quantum mechanics, in the 1930s. Physicists have hunted for these monopoles for years because of the key role they play in the theory of the universe - but without success.
Ordinary water ice (H2O). has the strange property that the hydrogen (h) atoms remain disordered even at the absolute zero temperature. Spin ice is a substance composed of atoms like tiny magnets which show exactly the same pattern of disorder as ice's hydrogens (the name 'spin ice' arises because the atoms' magnetism is caused by spinning electrons). It turns out that if you lived inside a lump of spin ice - if spin ice was your universe - then you WOULD be able to isolate magnetic monopoles, as they really exist within the material. This was recently proved by scientists from Oxford, Dresden and Princeton. However, these monopoles cannot escape the material so are not exactly the elementary monopoles from the dawn of time dreamed of by particle physicists.
Nevertheless, as stressed in the article, if we can understand the existence of monopoles in spin ice, why not in the universe as a whole? The monopoles are not fundamental, but are nonetheless remarkable.
"When we discovered spin ice in 1997" says Professor Bramwell, "we never expected that it would contain anything so remarkable as magnetic monopoles, but studying this amazing material has taught us that in science, nothing is impossible!"
Tiny magnetic poles that can move around a lump of matter are of interest for another reason: they might be exploited in futuristic memory elements for computers. Research of this type, on so called "artificial spin ice" magnetic arrays, is continuing at the London Centre for Nanotechnology and elsewhere.