A Surprising Turn in Search for Magnetic Monopoles

• The search for magnetic monopoles has consumed the field of condensed matter physics for nearly a century.
• Now an international team of scientists from the U.K. and China have found emergent magnetic monopole behavior in a hematite, an iron-oxide component of rust.
• While this doesn’t prove whether or not magnetic poles can be truly separated, it could open the door to new data storage and computing technologies.

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Magnetic monopoles are a complicated concept with a deceptively simple name. At their most basic, these theoretical elemental particles are exactly what they sound like—magnets with only one pole instead of the usual two. But that simple moniker falls short of conveying the century-long search for this ever-elusive particle.

Usually, when you split a bar magnet in two, the new pieces form new poles and exhibit magnetic field lines the same way as before. In classical physics, it’s impossible to actually create a magnetic monopole, but the revolution of quantum mechanics in the early 20th century began to unravel that long-established assumption. However, nearly a century after English physicist Paul Dirac (who also correctly hypothesized the presence of antimatter) first theorized their existence, scientists still haven’t found magnetic monopoles in the observable universe.

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This search for a hypothetical object has instead led some physicists down different exploratory paths to find electromagnetic phenomena that appear to act like monopoles— some kind of virtual magnetic monopole. In a new study published in the journal Nature Materials, scientists from the University of Cambridge, the University of Oxford, and the National University of Singapore captured the first naturally occurring magnetic monopoles emerging from collective electron behavior in flecks of hematite, a type of iron oxide (a.k.a. rust).

“These monopoles are a collective state of many spins that twirl around a singularity rather than a single fixed particle, so they emerge through many-body interactions,” University of Oxford’s Hariom Jani, a co-author of the study, said in a press statement. “The result is a tiny, localized stable particle with diverging magnetic field coming out of it.”

The discovery of this new class of magnetic monopole can be attributed to two ideas. The first is a concept known as “emergence,” which was first popularized by Nobel laureate Philip Anderson in 1972 in an essay titled “More Is Different.” That essay states that, in condensed matter physics, the sum of individual physical pieces could exhibit different properties from its parts.

The second idea involved the study of antiferromagnets with what’s called “diamond quantum magnetometry.” This technique allows for the examination of the spin of a single electron on the tip of a diamond needle, which in turn allows researchers to measure its magnetic field as its impacts (in this case) hematite. Crucially, the technique pulls this off without affecting the behavior of the electron itself.

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“The challenge has always been direct imaging of these textures in antiferromagnets due to their weaker magnetic pull,” University of Cambridge’s Anthony Tan said in a press statement. “But now we’re able to do so, with a nice combination of diamonds and rust.”

Using these two techniques, the scientists discovered “hidden patterns of magnetic charges” that included expected dipoles and quadrupoles, but also monopoles. As Scientific American notes, this discovery doesn’t solve the quantum question of whether a magnet’s poles can be separated. But it could lead to the development of next-gen storage techniques, known as racetrack memory or ultra-efficient computing devices.

The next big thing in computing could be powered by the incredibly small quantum whirls of magnetic monopoles.