We demonstrate room-temperature ferromagnetism in germanium counter-doped with manganese and arsenic at concentrations up to approximately 2.1 Ã 1020Â at/cm3: these values are one order of magnitude lower than those at which ferromagnetic behavior has previously been observed. Synthesis proceeded by ion implantation at 513Â K followed by annealing in argon at 673Â K. High resolution TEM, STEM, and EDX show single-phase diamond cubic material lacking Mn or As precipitates. These findings are consistent with the prediction of Chen et al. that counter-doping with approximately equal concentrations of a single-electron donor permits Mn, a two-electron acceptor, to be incorporated at high enough concentrations to yield a diluted magnetic semiconductor with a Curie temperature above room temperature.
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