This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Time-reversal symmetry is an exotic behavior found in systems whose internal physics looks different when running forward versus backward in time. For some time, physicists have searched for this behavior in systems with almost no overall magnetization.
Such phases are highly prized for spintronics, where information is carried using the quantum spins of electrons. Through new research published in Physical Review X, a team led by Pengcheng Dai at Rice University observed a strain-sensitive quantum effect in one such material that could bring practical spintronic devices a step closer. In most familiar magnets, time-reversal symmetry is broken by aligning large numbers of electron spins in the same direction, producing a strong overall magnetic field.
But in one newer class of materials, called "altermagnets," time-reversal symmetry can be broken while spins largely cancel out, leaving almost no net magnetization. This was recently discovered in a hexagonal form of manganese telluride. In the process, however, the material naturally splits into multiple magnetic "domains," whose magnetizations each point in different directions.
As a result, these signals overlap and obscure the underlying magnetic structure, making the effect especially difficult to isolate and control. Dai's team got around this by studying the material's anomalous Hall effect: a sideways voltage that appears when current flows through a magnetic material. Rather than being produced by an external field, this voltage is generated by the material's internal magnetic structure.
The researchers found that manganese telluride shows this effect spontaneously, confirming that time-reversal symmetry is indeed being broken despite its near-zero magnetization. This gave them a measurable signal to work with and a way to probe how the effect could be controlled. To get a clean look at that signal, the team physically stretched the material along one direction.
This forced the competing magnetic domains to merge into one, letting the team clearly resolve the material's true magnetic structure for the first time. Even more strikingly, by tuning the amount of strain, they found that they could flip the sign of the Hall signal entirely, switching its polarity without disturbing the underlying magnetic order. The team calculates that a mere 1% change in strain has an effect comparable to changing the temperature by around 150 degrees, a far more practical control method for real devices.
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