Chromium dioxide CrO2 nanoparticles with size below 4 nm were chemically synthesized. In contrast to the bulk compound, which undergoes a ferromagnetic transition at 390 K, SQUID data of the highly-disordered nanoparticles follow approximately a Curie-Weiss fit. The low temperature specific heat is dominated by a much larger ferromagnetic spin-wave term than that of bulk CrO2. A spin-glass-type transition occurs near 6.5 K, based on the observation of a cusp in the temperature dependence of the ac susceptibility, accompanied by a small specific heat anomaly. ? 2006 American Institute of Physics.
