In a solid, atoms vibrate, transmitting sound. Sometimes this wave doesn't run straight but curls into a spiral, like a corkscrew entering a cork. In ordinary crystals, such 'sound vortices' are known, but in magnetic materials they had long eluded detection. Now, neutron spectroscopy, a method where a neutron beam probes atomic motions and their magnetism, has captured these elusive vortices.
In a crystal of zinc, iron, and molybdenum, cooled to -224°C, the spiral waves gained their own magnetic field. They split into two distinct tones, and an external magnet shifted the frequency, like a hand tuning a guitar. Similar vortices are created by bats for echolocation in fog, but here the vortices became magnets.
The biggest surprise: these 'sound magnets' can be controlled just by changing the magnetic field. This opens the way to transmitting information without electric current — by the dance of atoms alone.
Phonons are simply coordinated vibrations of atoms, yet they behave like particles with mass, momentum, and now even a magnetic moment.