Imagine computer hardware that is blazing fast and stores more data in less space. That’s the promise of antiferromagnets, magnetic materials that do not interfere with each other and can switch states at high speed, opening the door to advanced computing and quantum applications.

Magnetism comes from unpaired electrons, tiny particles that orbit an atom’s nucleus. Each electron has a property called spin, which can point up or down. In standard ferromagnets, the atomic spins point in the same direction, creating a strong magnetic field. In antiferromagnets, neighboring spins point in opposite directions, canceling each other out and yielding no net magnetism.

Flipping individual spins in an antiferromagnet requires very little movement of magnetization, which allows ultrafast processing. Antiferromagnets can switch states trillions of times per second, compared with billions for ferromagnets. With net zero magnetism, antiferromagnets can be placed very close together without repelling or attracting each other, allowing more data to be stored in a small space. 

But their zero net magnetism also makes it challenging to detect the magnetic state of antiferromagnets, a key step for reading or writing information. 

Now, University of Delaware researchers have devised a way to “see” the magnetic state of antiferromagnets. Their method promises to advance efforts toward using these materials in next-generation computing technologies and quantum applications. The work, led by Chitraleema Chakraborty, assistant professor of materials science and engineering, appears in ACS Nano. 

Lighting up the undetectable

An unmagnetized metal, such as a paperclip, can become magnetic by sitting in the magnetic field of a ferromagnet, which nudges its electrons into alignment. 

The researchers applied a similar idea to antiferromagnets. They placed a second material that can change in response to its magnetic environment extremely close to an antiferromagnet. The proximity is critical because the magnetism from an antiferromagnet fades away within a few nanometers, a distance roughly 40,000 times thinner than a human hair. 

The team layered an atomically thick, light-responsive semiconducting material on top of an antiferromagnet. Tiny crystal defects in the semiconductor layer act as light-emitting sensors. As these defects respond to the magnetic field, changes in their light emissions reveal the antiferromagnet’s state.

“When you bring the defects close to the antiferromagnet, they shift their energy levels in a way that changes the light emitted,” said first author Muhammad Hassan Shaikh, a doctoral candidate in physics in the Chakraborty lab. “From those light changes, we can tell how the magnet is aligned and how strong the local field is.”