For decades, scientists recognized only two main types of magnets.
One is the well-known ferromagnetic material, the kind found in refrigerator magnets and countless everyday devices. The other is antiferromagnets, whose magnetic properties are hidden at the atomic level but are of increasing interest because of their potential use in advanced technologies.
More recently, researchers have identified a third category known as alternating magnets. First proposed within the past decade, these materials may combine some of the most useful properties of both ferromagnets and antiferromagnets, potentially opening the door to faster and more energy-efficient electronics.
Now, physicists at the University at Buffalo have proposed a new quantum sensing approach that makes identifying alternating current magnets much easier.
The proposed method is described in. physical review letterit is possible to detect how a suspected metamorphic magnet affects tiny magnetic defects inside nearby diamonds. By monitoring how a defect’s magnetic signal relaxes over time, researchers may be able to identify telltale signs of magnetism.
“This could be the first building block of a new generation of experiments to determine whether materials are alternating magnets,” says corresponding author Dr. Jameel Marino, assistant professor in the Department of Physics in UB’s College of Arts and Sciences. “Alternating magnets could completely revolutionize the way information is transmitted, but to confirm whether this elegant theory is true, we need experiments to identify alternating magnets and confirm that they behave as scientists predicted.”
Co-authors of the study include Marino’s former colleagues Libor Schmejkal and Jairo Sinova of the Johannes Gutenberg University of Mainz, the researchers who originally proposed the alternating magnet concept.
“This sensing technology could be a very important tool for exploring alternative magnetic material candidates,” says Synova. “It offers an advantage over traditional experimental techniques by detecting subtle directional magnetic patterns across different regions of the material without significantly disturbing the material.”
What is the difference between alter magnets?
The idea of alternating magnetism emerged in 2019 when researchers in Mainz encountered behavior that neither ferromagnets nor antiferromagnets could explain.
Their calculations suggested that ruthenium dioxide should have no overall magnetization, similar to antiferromagnets. However, when exposed to an electric current, it appeared to behave more like a ferromagnetic material.
This unexpected result led to the development of the altermagnet concept.
In conventional magnets, the atoms and their electron spins are usually arranged in a relatively simple pattern. In ferromagnets, adjacent electron spins point in the same direction, creating an external magnetic field. Because these spins can be switched relatively easily, ferromagnets are widely used to store information.
Antiferromagnets work differently. Adjacent spins point in opposite directions, so their magnetic effects cancel each other out. Although this arrangement is more difficult to control, it allows states to be switched more quickly, making antiferromagnets attractive for future information processing technologies.
AC magnets are somewhere in between. Similar to antiferromagnets, the overall magnetism cancels out. However, the arrangement of atoms within the material causes the electrons to behave in a manner typically associated with ferromagnets.
“This arrangement allows alternating magnets to combine the fast switching behavior of antiferromagnets with some of the more easily controllable electronic properties of ferromagnets,” Marino says.
Detecting hidden magnetism using diamond defects
Researchers in Mainz and elsewhere have already reported experimental signatures of alternating current magnetism in some materials. Theoretical research suggests that this class may grow even larger, with over 200 substances potentially qualifying as modified magnets. This is more than twice the number of known ferromagnetic materials.
To help identify these candidates, Marino’s team developed a proposed quantum sensing technique.
This approach relies on diamonds containing microscopic magnetic defects formed by nitrogen atoms and missing neighboring carbon atoms. These defects are highly sensitive to nearby magnetic activity.
In the proposed experiment, the researchers would rotate the defect’s magnetic spin in different directions and measure how quickly the defect relaxes. If relaxation occurs more rapidly in certain directions than in others, the behavior can reveal the complex spin arrangement expected in altermagnets.
An important advantage of this technique is that it is less disruptive than many existing methods used to study magnetic materials.
“You don’t want your measurements to cause large fluctuations in the material you’re studying, because it can make it difficult to tell whether you’re looking at the material’s natural behavior or experimentally generated behavior,” Marino says.
Aiming for faster and more efficient electronics
Marino emphasizes that the sensing system currently exists only as a theoretical proposal. The team developed it using a sophisticated model that simulates quantum mechanics, but experimental validation is still needed before researchers know whether it can reliably identify alternating current magnets.
“Effectively identifying magnetically variable materials is an important step toward someday actually using them in electronics,” Marino says. “Alternative magnets would make the transmission of information fundamentally more efficient, potentially reducing the scale of the technology and reducing power consumption.”
Additional co-authors include Dr. Hossein Hosseinabadi, a former graduate student in the Marino lab and now an independent distinguished postdoctoral fellow at the Max Planck Institute for the Physics of Complex Systems in Germany, and VASV Bittencourt from the University of Strasbourg/Max Planck Institute for the Physics of Light.
This research was supported by the German Research Foundation.
