Graphene is a sheet of carbon one atom thick. If you cut it into narrow strips, you get graphene nanoribbons. Their properties depend on how the strip is cut: just as from a single piece of fabric you can sew both a smooth tablecloth and a pleated skirt.
In the new work, chemists assembled a ribbon of asymmetric shape. In it, all free electrons ended up on one side, as if all the guests at a party crowded around one table. From such crowding, electrons began to behave coherently: their spins (tiny magnetic arrows) aligned in one direction. The ribbon became a magnet and stopped conducting current.
Calculations confirmed that electrons in the ribbon interact strongly with each other, and this interaction triggers magnetic ordering. This means that by changing the ribbon's shape, you can preset its magnetic properties. Such ribbons are like building blocks from which you can assemble materials with desired behavior.
Magnetic graphene ribbons could become the basis for spintronics — devices where information is carried not by charge but by spin direction. This is a path to faster and more energy-efficient chips.
The magnetic order in the ribbon appeared at room temperature, like a regular fridge magnet, but the ribbon is thousands of times thinner than a human hair.