Article Posted on : - Sep 05, 2009

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NEW DELHI (BNS): Researchers are stepping closer to finding the mysterious monopole – a magnetic pole without its opposite, which has long eluded physicists.

According to a New Scientist report Friday, two laboratory experiments using strange stuff called spin ice have provided the best evidence yet that “monopoles really are out there.”

There are several theories that predict the existence of monopoles. Among others, in 1931 the physicist Paul Dirac said it must be possible to separate the north and south poles of a magnet to give them a separate existence. But despite decades of searching moon dust, the debris from particle collisions and cosmic radiation for traces of a monopole, not one has been found.

Researchers have demonstrated that certain states of spin ice would create monopoles that rove about the crystal. Spin ice is a kind of crystalline material with essentially the same atomic arrangements as water ice. The monopoles would be seen as disturbances moving through the spins of atoms within the crystal.

Tom Fennell and his colleagues at the Laue-Langevin Institute in Grenoble, France, fired a beam of neutrons at a spin ice crystal to investigate how the crystals affected the neutrons' energy. They chilled the crystal to near-zero Kelvin – almost as cold as it is theoretically possible to get. The results implied that when the temperature of the crystal rose to around 1 kelvin magnetic monopoles were being formed within it.

In the experiment carried out by Jonathan Morris of the Helmholtz Centre for Materials and Energy in Berlin, Germany, and his colleagues – they watched how neutrons scattered off a spin ice crystal in a changing magnetic field.

The magnetisation of the particles within the crystals fell into alignment along trails through the crystal, suggesting that the magnetic field was pulling the monopoles apart. These trails are known as "Dirac strings", because Dirac predicted that cosmic monopoles would have just such a connection between them, the report said.

"To my mind there's now no question whatsoever: we have overwhelming evidence that these things are real," said Steve Bramwell of University College London.
That is good news for our biggest theories about how the universe came into being. Such "grand unified theories" or GUTs, which describe the earliest moments of the universe's existence, all require that monopoles exist, but at energies beyond the reach of particle accelerators.

The spin ice observations are the closest thing to confirmation of the GUT picture that we are likely to get for the foreseeable future, said Morris.

Spin ice crystals might teach us more about the conditions of the early universe, however, said Bramwell. “If you were forced to live inside a block of spin ice, you wouldn't be able to tell the difference between these monopoles and the cosmic ones.”