The ultimate limit of miniaturized classical data storage would be to use single-atom magnetic bits. Holmium atoms are seen as promising candidates because they have long magnetic relaxation times, so they do not easily lose their information. Fabian Natterer et al. now achieve the reading and writing of the magnetism of single holmium atoms, using a scanning tunnelling microscope, and show that individual atoms keep their state for many hours. They use these atoms to make a two-bit memory, to which they write the four possible states. They then use nearby magnetic iron atoms as sensors to confirm the magnetic states. This work suggests that single-atom magnetic memory should be possible.
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