A ruthenium oxide film is like a soap bubble film stretched over a frame, but made of atoms. For a long time, it was believed that in this film, ruthenium atoms align in a magnetic order, like compass needles pointing in opposite directions. This order was dubbed altermagnetism, and great hopes were placed on it for future electronics.

But when researchers directed X-rays at the film and observed how they were absorbed depending on polarization, the picture did not match expectations. The signal, which should have changed upon heating or when the magnetic field direction was reversed, remained almost the same. Calculations showed that this signal pattern arises not from magnetic order but from the fact that the crystal lattice has low symmetry — the atoms are arranged slightly "skewed," like bricks in a wall laid at an angle.

Thus, the ruthenium film lost its magnetic status. But the method itself — X-ray linear dichroism — proved to be a reliable tool: it distinguishes between true magnetic order and mere crystal geometry. This is important to avoid wasting effort searching for altermagnets where they do not exist and to focus on real candidates.