A sighting, of sorts, of separate north-south magnetic poles

Editor’s note: The original online version of this story was previously posted.

Magnets are remarkable exemplars of fairness—every north pole is invariably accompanied by a counterbalancing south pole. Split a magnet in two, and the result is a pair of magnets, each with its own north and south. For decades researchers have sought the exception—namely, the monopole, magnetism’s answer to the electron, which carries electric charge. It would be a free-floating carrier of either magnetic north or magnetic south—a yin unbound from its yang.

Field Day:
 Magnets always have a north pole and a south pole. Physicists have managed to separate them in unusual materials called spin ices, enabling each pole to move freely.
Cordelia Molloy Photo Researchers, Inc.

Two research groups—one led by Tom Fennell of the Laue-Langevin Institute in Grenoble, France, and the other by Jonathan Morris of the Helmholtz Center Berlin for Materials and Energy—have offered experimental evidence that such monopoles do in fact exist, albeit not as electronlike elementary particles. Rather they exist as unbound components inside so-called spin ices. These man-made materials take their name from their similarity to water ice in terms of their magnetic nature. The French-led team experimented with holmium titanate and the Germany-based group, dysprosium titanate.

Claudio Castelnovo, a physicist at the University of Oxford on the Morris team, explains that the compounds offer a peculiar combination of order and freedom that facilitates the dissociation of the poles. Internally, the tiny magnetic components in spin ices arrange themselves head to tail in strings, like chains of bar magnets stretching across a table in different directions. In a very cold, clean sample, those strings form closed loops.

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