A thin film of the compound of manganese, bismuth, and tellurium resembles a layered cake: each layer is an atomic plane, and the magnetic moments within the layer are aligned like compass needles. At room temperature, these needles hold formation, but just heating the sample to 45°C makes the order start to fall apart.

Random defects in the crystal act like tiny magnets that pull neighboring needles in different directions. The more such defects, the easier it is for heat to destroy the overall order. Scientists compared samples with different defect densities and saw: the magnetic properties degrade with heating more strongly when there are more defects.

This discovery explains long-standing disagreements between laboratories: some obtained 'ideal' magnetic states, others did not. Now it is clear that it all comes down to heat and defects. Therefore, to create devices based on this material, one must strictly control temperature and crystal quality.