Magnetic moments in a crystal are like compass needles fixed at lattice sites. In the normal state, they line up in neat order, but if an electromagnetic wave strikes the crystal, the needles start to sway, like wheat stalks in the wind. These oscillations are called magnons, and they carry energy without the atoms themselves moving.
In the layered material CrOCl (chromium oxychloride), these oscillations turn out to be especially diverse. Under a weak external field, the needles sway in one pattern, but as the field strengthens, their order breaks: some needles tilt sideways, and new types of oscillations appear. At a certain point, two different waves coexist in the crystal, like two different dances in the same room.
This flexibility stems from competition between exchange interactions (the tendency of needles to align) and anisotropy (the preference for certain directions in the crystal). By changing the external field, one can switch the material between different magnetic phases, and with them, the properties of magnons. This is useful for spintronics, where information is carried not by electrons but by magnetization waves.
Magnons behave like particles: they can be thought of as quanta of vibrational energy, and they obey Bose–Einstein statistics.