RIKEN physicists have discovered for the first time why the magnitude of the electron flow depends on direction in a special kind of magnet1. This find could help to realize future low-energy devices.
In a normal magnet, all the spins of electrons point in the same direction. In a special class of magnets known as chiral magnets, the electron spins resemble a spiral staircase, having a helical organization.
This structure imparts chiral magnets with special magnetic and electronic properties. For example, electrons can preferably flow along them in one direction but not another. This effect is akin to what occurs in diodes, except it occurs within a single material rather than in a junction between two semiconductors.
Chiral magnetics could have practical applications since they can host tiny magnetic whirlpools known as skyrmions, which are promising for realizing memory devices that have low energy consumption.
Several mechanisms have been proposed for the direction-dependent flow of electrons in chiral magnets, but no previous study had successfully separated and assigned multiple mechanisms in a single material.
Understanding what causes the effect has been important, as it would help physicists to exploit it better. "If we can determine the mechanism, it would give us more control of the system," explains Daisuke Nakamura of the RIKEN Center for Emergent Matter Science.
Now, Nakamura and co-workers have found that two separate effects can account for the direction-dependent flow of electrons in a chiral magnet.
Which effect dominates depends on the temperature and the magnetic field. In some cases, electrons traveling in one direction are scattered more frequently by magnetic quasiparticles with chirality, whereas those traveling in the other direction are not scattered so much.
The other mechanism occurs during coupling between mobile electrons and helical spins of static electrons that contribute to the symmetry-breaking energy map of mobile electrons in the chiral magnet.
Experimental measurements alone were not enough to determine the mechanisms-theoretical calculations were also required. "Clarifying the mechanism is very challenging," says Nakamura. "We had to enlist the help of theoretical physicists that are based at RIKEN and collaborative research groups."
For the investigation, the team chose a chiral magnet made of the three metals cobalt, zinc and manganese because, unlike many chiral magnets, this type can show a helical spin arrangement at a wide range of temperatures, including room temperature.
However, the researchers anticipate that their findings will apply to other systems and materials, opening the door to new discoveries in the one-way conduction of electricity.
They now intend to investigate what happens when they vary the makeup of the chiral magnet by tweaking the ratio of the three metals.
Daisuke Nakamura of the RIKEN Center for Emergent Matter Science © 2025 RIKEN
