| National Institute of Standards and Technology, www.nist.gov |
Scientists have been searching for a monopole — a magnet with just one pole, not a north and south pole — ever since physicist Paul Dirac theorized their existence. A team of scientists working at the National Institute of Standards and Technology’s Center for Neutron Research claim they have come up with one, though it is not as small as the one Dirac predicted.
The NIST team created their monopole by combining oxygen, titanium, and dysprosium and freezing the compound to nearly absolute zero. This formed it into “spin ice,” a tetrahedron-shaped crystal having ions at its four corners with spins that balance — two spin inward and two spin outward. Using a neutron beam, the team was able to knock one of the spins askew so that three ions spun inward, creating a monopole, “or at least its mathematical equivalent,” said one scientists. Because each tetrahedron shares its four tips with adjacent tetrahedrons, flipping the spin in one tip creates an anti-monopole in an adjacent tetrahedron.
The team says studying the spin ice will let them test predictions about monopoles. For example, Maxwell’s equations predict that monopoles should obey Coulomb’s Law and their interactions should decrease as they get farther apart.