Are there magnetic charges or not?

Two research groups independently unveil the ancient mystery of electromagnetism

Magnetic monopoles

Berlin / Grenoble (France) - Electric charges can be separated into positive and negative, this trick doesn't work with magnets. Even if you cut a magnet in half again and again, the fragments immediately form a magnetic north and south pole. This principle of physics no longer applies. Independently of one another, physicists have now succeeded in proving, with two experiments in Berlin and Grenoble, that magnetic monopoles actually exist. Both groups publish their results in a pre-publication of the journal "Science".

"We are describing new, fundamental properties of matter," says Jonathan Morris from the Helmholtz Center Berlin for Materials and Energy (HZB). Together with colleagues from Dresden, Argentina and Great Britain, he found the magnetic monopoles previously believed to be non-existent in a crystal made of dysprosium titanate. Because of the similarity of the crystal lattice to the molecules in frozen water, this substance is also called spin ice. Using scattered neutrons, which the researchers directed to their sample in the Berlin research reactor, they discovered that the magnetic moments in the spin ice were arranged to form intertwined tubes, the spin spaghetti.

With an external magnetic field, the researchers have now taken the essential step. They were able to realign the spin spaghetti and demonstrate a separation of the magnetic poles. As a result, individual spin spaghetti with magnetic monopoles at their ends became visible at a temperature of around minus 272 degrees Celsius. The characteristic features of these magnetic monopoles could be observed in parallel by measuring the heat capacity of the spin-ice structure. And completely independently of the Berlin research group, French, British and German scientists examined another spin ice made from holmium titanate. Their results, which they obtained with neutrons at the Laue-Langevin Institute in Grenoble, also provide conclusive evidence of the existence of magnetic monopoles.

With these two experiments an old, physical mystery is finally unveiled. Because as early as 1931 Paul Dirac predicted the existence of monopoles as a source of magnetic fields in a theory. He was essentially driven by the apparent contradiction that electrical charges can be separated, but magnetic poles cannot. Dirac's calculations resulted in so-called Dirac strings, which meander through a material like tubes and have magnetic monopoles at their ends. With the spin spaghetti they have now observed, the Berlin researchers come very close to the idea of ‚Äč‚Äčthese Dirac strings.

After this groundbreaking discovery, the first ideas to use magnetic monopoles for high-density data storage are already emerging. At the same time, it is rumored in the physicist community that this discovery is definitely worthy of a Nobel Prize. But first, the experiment would have to be repeated elsewhere and confirmed with the same results. Since the monopoles only occur in the spin ice and not in isolation, a technical application is rather a long way off.