In a ballroom, the music changed, and the couples that had been moving along straight lines suddenly spun off into whirls. That is how a crystal of Fe3Ge behaves when it is heated above 375 kelvins, which is roughly a hundred degrees Celsius. Below that threshold, the tiny magnetic arrows in the crystal lie flat, like couples in a slow waltz. Above it, the arrows stand on end, and magnetic whirls appear in the material. Scientists call them skyrmions.
The Fe3Ge crystal is woven from iron and germanium atoms, and its pattern looks like a basket of triangles. In such a pattern, electrons move in an unusual way, as if they had no mass, and because of this the material carries current across the applied voltage even without a magnet. The effect is called the anomalous Hall effect, and at room temperature it is very strong. The scientists cut a thin plate from the crystal and shone a beam of electrons through it. The image revealed whirls twisting both left and right in equal numbers. That means the whirls are held together by the material's own magnetic forces, not by an external field.
The whirls persist from 375 to 650 kelvins, one of the widest temperature windows among all the materials where they have been found. Such a whirl can be nudged with a tiny current, and it will not fall apart, so its position can serve as a zero or a one in memory. Conventional hard-drive memory requires more energy and more space. True, at room temperature the whirls in Fe3Ge do not appear yet, because the magnetic arrows are still lying flat. The next step is to replace some of the iron or germanium atoms with others, so that the arrows stand on end at 300 kelvins already.
The Fe3Ge crystal is a rare place where two different dances meet. One is whirls in space, visible under a microscope. The other is whirls in the world of electronic states, which give themselves away through the anomalous Hall effect. Previously they were studied separately, but here they spin together. Perhaps it is in materials like these that memory will be born that needs no refrigerator.
Skyrmions are named after the British physicist Tony Skyrme, who proposed them in 1962 as a model for describing nuclear particles. Today these "particles" live in magnetic crystals and can be smaller than one hundred nanometers.
In Arthur C. Clarke's novel The City and the Stars, information is stored in crystal lattices that rearrange almost without energy cost. Magnetic skyrmions in Fe3Ge are a real step toward such memory: they are tiny, robust and move under ultralow currents.