Figure 1: High-pressure evolution of the structural and magnetic properties of CuO.
From: Room-temperature spin-spiral multiferroicity in high-pressure cupric oxide
(a) Schematic view of the tetrahedral environment of oxygen atoms in CuO and definition of the largest (Jz) and smaller magnetic superexchange couplings (Jx, Ja and Jb). The super-superexchange magnetic coupling, J2a, corresponds to the second-neighbour interaction of the edge-sharing chains, defined by the first-neighbour interaction, Ja. Oxygen atoms are represented by small red dots, and the Cu2+ sites are depicted as filled and open dots, representing up-spin and down-spin, respectively. (b) Pressure dependence of the volume of CuO. The experimental values, deduced from a Birch–Murnaghan equation of state fitted to data of nanocrystalline CuO up to a pressure of 17 GPa (ref. 21), are compared with those calculated by DFT. (c) Pressure dependence of the magnetic exchange couplings of CuO. Positive and negative values represent antiferromagnetic and ferromagnetic interactions, respectively. The J’s in the grey area are ferromagnetic. The uncertainty in the DFT Jij values is between 1.2 and 2.5 meV (that is, smaller than the symbols).
