Individual magnetic ‘charges’ – equivalent to the north and south poles of a magnet – have been observed inside a crystalline material called spin ice (Image: STFC) How to make a monopole

The magnetic equivalent of electricity, dubbed “magnetricity”, has been demonstrated experimentally for the first time. Just as the flow of electrons produces electrical current, individual north and south magnetic poles have been observed to roam freely, generating magnetic “current”.

The result could lead to the development of “magnetronics”, including nano-scale computer memory.


Magnets normally have two poles, north and south, that are inseparable. Cutting a magnet in half only results in each piece developing its own north and south pole. That is true even if one disassembles a magnet all the way down to its individual atoms, since each behaves as a tiny bar magnet with two poles.

But physicists have theorised that magnetic monopoles – individual north and south poles that are not bound in pairs and can move independently of one another – could form inside a crystalline material called spin ice.

Changing patterns

The individual atoms would still have both north and south poles. But patterns in their orientation would propagate through the material and look just like little magnetic poles roaming around (see illustration). These patterns would effectively be monopoles, as far as any measurements are concerned.

In September, two teams of physicists fired neutrons at spin ices made of titanium-containing compounds chilled close to absolute zero. The behaviour of the neutrons suggested that monopoles were present in the material.

Now, another team has managed to measure the amount of magnetic “charge” on the monopoles and to measure magnetic analogues to electric current for the first time. The team calls the motion and interaction of monopoles “magnetricity”.

The experiment, reported in Nature, was led by Steven Bramwell of the London Centre for Nanotechnology in the UK. Bramwell was a member of a team, led by Tom Fennell of the Laue-Langevin Institute in Grenoble, that reported neutron results in September.

Magnetic ‘charge’

To get more detailed information on the monopoles than had previously been possible, Bramwell’s team injected muons – short-lived cousins of electrons – into the spin ice. When the muons decayed, they emitted positrons in directions influenced by the magnetic field inside the spin ice.

This revealed that the monopoles were not only present but were moving, producing a magnetic current.

It also allowed the team to measure the amount of magnetic charge on the monopoles. It turned out to be about a 5 in the obscure units of Bohr magnetons per angstrom, in close agreement with theory, which predicted 4.6. Unlike the electric charge on electrons, which is fixed, the magnetic charge on monopoles varies with the temperature and pressure of the spin ice.

Shivaji Sondhi of Princeton University in New Jersey, a spin ice researcher who is not a member of Bramwell’s team, called the new achievement “a triumph of a bold experimental foray” in an accompanying commentary in Nature. “The experiment itself and the determination of the charge of magnetic monopoles are striking.”

Shrinking memory

Data is stored on computer hard discs by magnetising their surfaces in patterns that represent 1s and 0s. Bramwell speculates that monopoles could one day be used as a much more compact form of memory than anything available today, given that the monopoles are only about the size of an atom.

“It is in the early stages, but who knows what the applications of magnetricity could be in 100 years time,” he says.

The monopoles in the spin ice are not the same as cosmic monopoles, fundamental magnetic particles theorised to have been forged in the big bang that have never been observed.

Journal reference: Nature (DOI: 10.1038/nature08500)