A gentle mechanical squeeze on a tiny iron sulfide crystal just revealed something researchers had not expected: two of the material’s strangest properties shrink together in perfect lockstep. The finding gives scientists their clearest look yet at how a newly recognized class of magnets actually works.
Researchers at Rice University compressed a crystal of hexagonal iron sulfide and watched its faint magnetic signal and an unusual electrical effect weaken in tandem. The findings were published in the journal Advanced Materials.
A magnet that breaks the mold
The material belongs to a group called altermagnets, which combine traits from two more familiar magnetic types. Like antiferromagnets, most of their internal magnetic moments cancel each other out, so they produce no strong external magnetic field. Yet they can still influence moving electrons in ways that could prove useful for future electronic devices.
The hexagonal iron sulfide studied here carries a very small leftover magnetic moment despite that internal cancellation. It also generates an unusual electrical signature called the anomalous Hall effect. Current flowing through the material produces a sideways voltage even without any external magnetic field applied.
Two signals, one squeeze
Corresponding author Pengcheng Dai said the material lets researchers watch its tiny magnetic signal and its electrical signal at the same time. He said squeezing the crystal along one direction made both signals shrink together, a sign the two effects are closely connected.
The team built a device that compressed the crystal from a single direction, then tracked both properties as pressure increased. The small magnetic moment and the sideways voltage both weakened steadily. The much larger underlying magnetic order beneath them stayed essentially unchanged throughout the experiment.
Researchers turned to neutron beams at Oak Ridge National Laboratory to see what pressure was actually doing inside the crystal’s magnetic structure. The measurements showed the basic magnetic arrangement stayed intact, but the squeeze shifted which magnetic orientations the material favored internally.
The crystal holds several nearly equivalent directions its magnetic moments can point toward. Because the energy difference between those directions is tiny, even modest pressure can tip the balance toward one orientation over another. That makes the material unusually easy to tune mechanically.
An open question remains
The results also speak to a long-standing question about why the material generates its unusual electrical signal. One common explanation, known as Berry curvature, involves how electrons move through the crystal’s electronic structure. First author Weiliang Yao said the new measurements don’t rule that explanation out. Instead, they show the electrical signal and the tiny magnetic moment are strongly linked, leaving open exactly why that link exists.
Dai said controlling such effects with simple mechanical strain could eventually prove useful for spintronics. That field aims to harness electron spin for storing or processing information with less magnetic interference and lower energy use than many conventional technologies.