The crystal of RbMn6Bi5 resembles a five-story building of manganese atoms, where the residents on each floor form a pentagon. At room temperature, the magnetic moments of the atoms fluctuate chaotically, like compass needles during a magnetic storm. But cool the crystal below a certain temperature, and the needles suddenly freeze into strict order. This order, as the researchers found using nuclear magnetic resonance, turned out to be unexpectedly intricate.
Instead of a simple north-south alternation, the magnetic moments at the pentagon corners point in different directions, creating a complex pattern. The central manganese atom, meanwhile, carries no magnetic moment at all, like a stationary pole at the center of a carousel, around which the seats revolve. Such a pattern contradicts previous models that assumed uniform magnetization waves.
The most interesting part happens right next to this order. Even when the crystal is already cooled, strong magnetic fluctuations remain, like a frozen carousel that continues to tremble slightly. Such fluctuations, the scientists believe, may act as a glue for electrons: under high pressure, they help electrons pair up, leading to superconductivity. This resembles the mechanism at work in famous high-temperature superconductors based on copper and iron.
Thus, the manganese material joins the ranks of its distinguished relatives. Its magnetic architecture is not just a curiosity but a possible key to understanding how resistance-free superconductivity arises.
Manganese atoms in RbMn6Bi5 form pentagons, and at the center of each pentagon sits a manganese atom with no magnetic moment — a rare case of a 'magnetically empty' center in an ordered structure.