Diamond sensor proposal targets emerging class of magnets

University at Buffalo physicists have proposed a quantum sensing method that could make it easier to identify altermagnets, an emerging class of magnetic materials. The approach matters because University at Buffalo researchers say altermagnets may help support faster, more energy-efficient electronics if their predicted behavior can be confirmed in experiments.

The method, described in Physical Review Letters, would use a tiny magnetic defect inside diamond to detect signals from a nearby candidate material. According to the university, the sensor would look for directional changes in how the defect’s magnetic signal relaxes over time.

A third type of magnet

Scientists long grouped magnets mainly into two categories, the University at Buffalo said. Ferromagnets, the familiar kind used in refrigerator magnets and many devices, have neighboring electron spins that align and create an external magnetic field.

Antiferromagnets have neighboring spins that point in opposite directions, causing their magnetic effects to cancel at larger scales, according to the university. Researchers have studied them for advanced technology because they can switch states quickly, though they are harder to control.

Altermagnets were proposed within the last decade and are described by University at Buffalo researchers as combining traits from both groups. Like antiferromagnets, they lack overall magnetization, but their internal atomic structure can give electrons some behaviors associated with ferromagnets.

Jamir Marino, an assistant professor of physics at the University at Buffalo and corresponding author of the study, said the arrangement could pair the fast switching of antiferromagnets with more controllable electronic properties found in ferromagnets. He also said experiments are needed to show whether the theory matches how materials behave.

How the diamond test would work

The proposed sensor relies on a diamond defect made from a nitrogen atom next to a missing carbon atom, according to the research team. Such defects are sensitive to nearby magnetic activity.

In the proposed setup, researchers would rotate the defect’s magnetic spin in different directions and measure how quickly its signal relaxes. If that relaxation happens faster in some directions than others, the pattern could point to the spin arrangements predicted for altermagnets, the university said.

Jairo Sinova of Johannes Gutenberg University of Mainz, a co-author of the study, said the technique could help researchers study candidate altermagnetic materials. He said it may detect subtle directional magnetic patterns in different parts of a material while causing less disturbance than conventional methods.

Marino said avoiding strong disruption is useful because heavy-handed measurements can make it harder to separate a material’s natural behavior from effects caused by the experiment.

Still a theoretical proposal

The University at Buffalo said the sensing system has not yet been experimentally validated. The team developed the proposal through models that simulate quantum dynamics.

Researchers in Mainz and elsewhere have already reported experimental signs of altermagnetism in several materials, according to the university. Theoretical studies suggest more than 200 materials could qualify as altermagnets, which would be more than twice the number of known ferromagnetic materials.

The idea grew out of work in Mainz in 2019, when researchers studying ruthenium dioxide found behavior that did not fit the established categories, the university said. Their calculations indicated the material should have no overall magnetization, yet under electric current it appeared to act more like a ferromagnet.

The study’s authors include V.A.S.V. Bittencourt, Hossein Hosseinabadi, Sinova, Libor Šmejkal and Marino. The University at Buffalo said the research was supported by the German Research Foundation.

This story draws on original reporting from ScienceDaily.