Two magnets on a table either attract or repel — depending on how their poles are oriented. Inside each piece hide tiny regions where all the magnetic arrows point in the same direction. These regions are called domains, and their arrangement determines how the material behaves in an electrical circuit.

In altermagnets, a new class of materials, domains are trickier. The magnetic moments of neighboring atoms are not just opposite but also rotated in space in a special way. It's like rows of dancers moving in opposite phases, but each slightly turned. Until now, seeing this picture directly was impossible. The authors used a scanning quantum microscope with a diamond needle — an ultra-sensitive sensor that feels magnetic fields the way a finger feels the warmth of a radiator. This way, they saw domains in MnTe films down to a few atomic layers thick for the first time.

It turned out that the weak magnetization detected by the microscope originates at the film-substrate interface. It is this magnetization that is responsible for the anomalous Hall effect — the appearance of an electrical voltage across a conductor without an external magnet. By controlling the film thickness, one can tune this effect, and thus design future devices where information is carried not by charge but by electron spin.

So the quantum microscope became a window through which one can see how magnetic arrows dance in the depths of matter. And this dance, it turns out, can not only be observed but also directed, like a conductor changing the orchestra's rhythm with a wave of the baton.