Figure 1. Structural and magnetic properties of CuO at ambient pressure.

The experimental magnetic susceptibility¹⁴ is compared to a simulated one based on an S = 1/2 Heisenberg uniform chain model with J = J_z = -80.5 meV. The experimental susceptibility has been corrected by the temperature independent contribution χ₀, i.e. χ_exp(T) = χ_mol(T) – χ₀, with χ₀ = +20 × 10^-6 emu/mol, as found from the fit of the high-temperature magnetic susceptibility and a g factor of 2.095 obtained from EPR measurements²⁴. A progressive construction of the crystal structure and the magnetic ground state of CuO is shown, indicating the most important (J_z) and other (smaller) magnetic exchange couplings (J_x, J_a, J_b and J_2a). At low temperature (T < T_L), the CuO magnetic structure consists of FM and AFM arrangements along the [101] and [10-1] crystallographic directions The oxygen atoms are represented by small red circles, and the Cu²⁺ sites are depicted as filled and empty circles, representing up-spin and down-spin, respectively.