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October 9th, 2009

NIST researchers find way to produce molecule-scale monopoles

Published on October 9th, 2009 | By: pwray@ceramics.org

A team at NIST’s Center for Neutron Research, led by Hiroaki Kadowaki of Tokyo Metropolitan University, has found a way to produce molecule-sized monopoles, a feat that would allow the exploration of magnetic monopoles in the laboratory, not just on the chalkboard (the existence of monopole particles has been hypothesized for 80 over years).

The team created their monopoles through the clever manipulation of a compound made of oxygen, titanium and dysprosium. They first cool the compound to nearly absolute zero, at which point it forms “spin ice.”

The material freezes into tetrahedral crystals. The spin of the ions at each of the four tips of the tetrahedron normally align so that their spins are “balanced.” Two spins point inward and two outward. That’s where the researchers step in to alter the crystal. Using neutron beams, the team learned it could alter one of the spins so that instead three point in, one out, “creating a monopole, or at least its mathematical equivalent,” says Jeff Lynn, a NIST physicist.

The NIST groups says it was able to confirm the existence of a monopole through neutron scattering techniques.

Neutron scattering at the NCNR allowed the team to see the spin ice’s transition from its normal state (center) to the monopole state. Monopoles scatter neutrons in a telltale fashion indicated by the red arrows in (bottom.)

More precisely, they confirm the existence of monopole and “antimonopole” pairs. Explains NIST:

Because every crystal pyramid shares its four tips with adjacent pyramids, flipping the spin of one tip creates an “anti-monopole” in the next pyramid over.

“Maxwell’s equations indicate that monopoles should obey Coulomb’s Law, which indicates their interaction should weaken as distance between them increases,” Lynn says. “Using the spin ice crystals, we can test ideas like this.”


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