Researchers begin to crack magnetic mystery

A seven decade magnetic mystery involving space hunts and quantum probes could have ended thanks to an international research team.

Magnetism is normally associated with a dipole – but monopoles could one day give a new type of electrical circuit

The monopoles predicted are not elementary particles like protons or electrons but are disturbances of the arrangement of spins – similar to ripples on the surface of a pond.

“We can’t see the monopoles directly but what we can detect is their magnetic influence on their surroundings,” said Professor Andrew Boothroyd of Oxford University’s Department of Physics, an author of the Science paper. “It’s rather like the motion of a crowd as someone pushes their way through.”

The existence of the magnetic monopole was suggested by Paul Dirac back in 1931 but for the next seven decades physicists searched outer space and quantum collisions in vain for evidence of this separated magnetic charge.

Then, in 2007, an Oxford University team theorised that monopoles could exist in a strange material dubbed ‘spin ice’ – so-called because the atomic electrons within it carry ‘spin’, a property which causes them to behave like tiny bar magnets, and arrange themselves in a similar way to water molecules in water ice.

Now, scientists from the Institut Laue-Langevin in Grenoble, University College London and Oxford University, report in this week’s Science that their investigations have detected disturbances in the magnetism of a spin ice compound that strongly suggest the influence of magnetic monopoles.

The spin ice compound studied has very unusual magnetic properties – which helps explain why monopoles have not been found elsewhere – arising from a specific crystalline structure that allows a very large number of possible equivalent magnetic arrangements. The experiments used a technique called neutron scattering that makes it possible to look at the arrangements of spin at the atomic scale.

Professor Boothroyd said: “It’s perhaps not too far fetched to imagine that, rather as we can build electrical circuits using positive and negative electrical charge, we might find a way to build magnetic circuits using magnetic monopoles. It might one day lead to new types of memory elements, electrical circuits or sensor devices.”