Diamonds and rust rewrite physics textbooks

Researchers from Cambridge have identified magnetic monopoles in hematite, suggesting new possibilities for advanced, environmentally friendly computing techniques. This first-time observation of emerging poles in natural magnets could open new horizons in quantum materials research.

Researchers have discovered magnetic monopoles – isolated magnetic charges – in a material closely related to rust, a finding that could be used to power greener, faster computing technologies.

Researchers led by the University of Cambridge used a technique known as quantum diamond sensing to observe swirling textures and faint magnetic signals on the surface of hematite, a type of iron oxide.

Emerging monopolies and eddy textures

The researchers observed that magnetic monopoles in hematite appear through the collective behavior of many spins (the angular momentum of the particle). These monopoles slide through the swirling textures on the hematite surface, like small hockey pucks with a magnetic charge. This is the first time that naturally occurring monopoles have been observed experimentally.

The research has also shown a direct connection between previously hidden vortex textures and the magnetic charges of materials like hematite, as if there were a secret code linking them together. The results, which may be useful in enabling next-generation logic and memory applications, were published today (December 5) in the journal Nature materials.

A historical perspective on magnetic monopolies

According to the equations of James Clerk Maxwell, one of the giants of Cambridge physics, magnetic objects, whether refrigerator magnets or the Earth itself, should always exist as a pair of magnetic poles that cannot be isolated.

“The magnets we use every day have two poles: north and south,” said Professor Mete Atatori, who led the research. “On the 19th^y In the twentieth century, it was postulated that unipoles could exist. But in one of his foundational equations for the study of electromagnetism, James Clerk Maxwell disagreed with this view.

Attatori is head of the Cavendish Laboratory in Cambridge, a position previously held by Maxwell himself. “If monopoles do exist, and we can isolate them, it would be like finding a missing piece of a puzzle that was supposedly missing,” he said.

Emergence strategy and collaborative research

About 15 years ago, scientists proposed how monopoles exist in magnetic materials. This theoretical result relied on the extreme separation between the North and South Poles, such that each pole appears locally isolated in an exotic substance called spin ice.

However, there is an alternative strategy for finding monopolies, which involves the concept of emergence. The idea of ​​emergence is that the combination of several physical entities can lead to properties that are either more than or different from the sum of their parts.

Work with colleagues from Oxford university And the National University of Singapore, Cambridge researchers used emanation to detect monopoles spreading out in 2D space, sliding through vortex tissues on the surface of a magnetic material.

Vortex topological textures are found in two main types of materials: ferromagnets and antimagnets. Of the two, antimagnets are more stable than ferromagnets, but they are more difficult to study, because they do not have a strong magnetic signature.

Antimagnets and diamond quantum magnetometry

To study the behavior of antimagnets, Attatori and his colleagues used an imaging technique known as diamond quantum magnetometry. This technique uses a single spin – the inherent angular momentum of an electron – in a diamond needle to precisely measure the magnetic field on the surface of a material, without affecting its behavior.

In the current study, the researchers used this technique to look at hematite, an antimagnetic iron oxide material. To their surprise, they found hidden patterns of magnetic charges within the hematite, including monopoles, dipoles, and quadrupoles.

Co-author Professor Paolo Radelli from the University of Oxford said: “The existence of monopoles has been predicted theoretically, but this is the first time we have actually seen a 2D monopole in a natural magnet.”

“These monopoles are a collective state of many spins orbiting a singularity rather than a single stable particle, so they emerge through many-body interactions. The result is a small, localized stable particle emerging from it,” said co-first author Dr. Harium Jani, from the University of Oxford. varying magnetic field.

Co-first author Dr Anthony Tan, from Harvard University, said: “We have shown how diamond quantum magnetometry can be used to unravel the mysterious behavior of magnetism in 2D quantum materials, which may open new areas of study in this field.” Cavendish Laboratory. “The challenge has always been to directly image these tissues in antimagnets because of their weak magnetic pull, but now we are able to do it, with an exquisite combination of diamond and rust.”

The study not only highlights the potential of diamond quantum magnetometry, but also underscores its potential to detect and investigate hidden magnetic phenomena in quantum materials. If controlled, these swirling tissues covered in magnetic charges could run computer memory logic extremely quickly and energy efficiently.

Reference: “Detection of emerging magnetic charge in antimagnets using diamond quantum magnetometry” by Anthony KC Tan, Harium Jani, Michael Hogan, Lucio Stefan, Claudio Castelnuovo, Daniel Brund, Alexandra Jim, Annika Michnic, Matthew SJ Fiore, Helena s. Knowles, Ariando Ariando, and Paolo G. Radelli and Miti Atatori, December 5, 2023, Nature materials.
doi: 10.1038/s41563-023-01737-4

The research was supported in part by the Royal Society, the Sir Henry Royce Institute, the European Union, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).