Alexandre Ivanov

Drop a stone into a pond, and ripples spread across the water. Magnets have waves too — only instead of water molecules, it's the directions of atomic magnetic arrows that oscillate. These waves are called magnons, and their behavior reveals a lot about the invisible forces between atoms.

Heat a crystal, and its atoms start to tremble more vigorously, like strings tightened or loosened. In a LaCoO3 crystal (a compound of lanthanum, cobalt, and oxygen), heating from 2 to 650 K triggers two major rearrangements: around 100 K, the magnetic state of cobalt ions changes, and around 550 K, the material transforms from an insulator into a…