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Stable magnets from single atoms
An important goal in molecular magnetism is to create a permanent magnet from a single atom. Metal atoms adsorbed on surfaces can develop strong magnetization in an applied field (paramagnetism). Donati et al. show that single holmium atoms adsorbed on a magnesium oxide film grown on a silver substrate show residual magnetism for temperatures up to 30 K and bistabilty that lasts for 1500 s at 10 K (see the Perspective by Khajetoorians and Heinrich). The atom avoids spin relaxation by a combination of quantum-state symmetry and by the oxide film preventing the spin from interacting with the underlying metal via tunneling.
Abstract
A permanent magnet retains a substantial fraction of its saturation magnetization in the absence of an external magnetic field. Realizing magnetic remanence in a single atom allows for storing and processing information in the smallest unit of matter. We show that individual holmium (Ho) atoms adsorbed on ultrathin MgO(100) layers on Ag(100) exhibit magnetic remanence up to a temperature of 30 kelvin and a relaxation time of 1500 seconds at 10 kelvin. This extraordinary stability is achieved by the realization of a symmetry-protected magnetic ground state and by decoupling the Ho spin from the underlying metal by a tunnel barrier.
