In a tiny magnet, information is encoded not in which way the arrow points, but in how the directions of its atoms alternate. In antiferromagnets, these arrows cancel each other out, so the material appears non-magnetic from the outside. The data is there, but you can't read it the usual way: the state is like a note written in invisible ink.

Physicists have found a way to make that ink visible. They brought the tip of a scanning probe close to the material's surface and illuminated it with infrared light. The light, concentrated at the tip, made electrons jump between energy levels. An electric current arose that changed direction depending on the hidden atomic order. They call this current the optical nonlinear anomalous Hall effect.

The experiment showed that this approach can not only read but also track the motion of magnetic domain walls. The scientists wrote information using a spin current and then read it out optically. The result is a full pair: electrical writing and optical reading.

Such memory does not generate external magnetic fields, so neighboring cells don't interfere with each other. Storage density could become very high, and switching could be faster than in conventional memory. The invisible note turns into readable code.