Specific-Heat Evidence for Quasi-1D Magnetic Order in CuO

High-precision specific-heat measurements of sintered CuO between 1.5 K and 340 K show a weak first-order anomaly at 212 K, a smaller than expected second-order anomaly at the Neel temperature T N = 230 K and substantial magnetic specific heat between T N and 340 K. We conclude that CuO is a quasi-one-dimensional system with Cu 2+ chains more than 70% ordered at T N and with intra-chain coupling constant J/k = 460 K. Several moments of the phonon spectrum are determined and at liquid-helium temperatures γ = 0.26 mJ/mol K 2 and Θ D = 396 K.