A study of the magnetic transitions in CuO: specific heat (1-330 K), magnetic susceptibility and phonon density of states

The specific heat C p (1-330 K) and magnetic susceptibility χ (5-250 K) of a CuO sample sintered and annealed in oxygen are presented. In contrast with some earlier results, we find: (i) an essentially zero linear term in the low-temperature specific heat (γ* < 0.05 mJ mol -1 K -1 ); (ii) a minor change in slope in the susceptibility curve and a critical point in C p at the antiferromagnetic transition ( T N = 229.5 ± 0.5 K); (iii) a first-order peak in C p at the commensurate-incommensurate transition ( T M = 212.6 ± 0.5 K, Δ H = 4.5 ± 0.3 J mol -1 ); (iv) a smooth variation of the susceptibility below T M . The phonon density-of-states is determined by inelastic neutron scattering on a single crystal at room temperature, thus enabling a separation of the lattice and magnetic contributions to C p . A large contribution due to short-range order is observed above T N , and it is concluded that CuO behaves as a 1D or 2D Heisenberg antiferromagnet. Thermodynamic functions are tabulated up to room temperature.