In a CrSBr crystal, the magnetic moments of atoms within each layer point in the same direction, but between layers they point in opposite directions. It's like a musical score where the notes in adjacent lines face different ways. This melody holds up to 132 kelvin, but then thermal motion destroys it. Physicists have found a way to rewrite the score: they bombarded the crystal with helium ions. These ions leave defects, like inserting rests into the sheet music, making the notes sound different.

To hear the new melody, the researchers directed a laser at the crystal and observed how the polarization of scattered light changed. In the pristine material, one characteristic of light changes sharply at 132 K, marking the transition to an antiferromagnetic state. In irradiated samples, two new changes appeared: at 40 K and 105–110 K. The first is likely related to ordering of defects, the second to a new magnetic order. The higher the irradiation dose, the stronger these changes. After double irradiation of a thick sample, the material completely ceased to be antiferromagnetic and became ferromagnetic — all spins aligned in one direction. Previously, this required strong magnets, but now simply bombarding the crystal with helium suffices. Such a method of controlling magnetism could be useful in future electronics.