Pressure effect on the magnetism of layered copper(II) compounds with interlayer spacing up to 40.7 Å:: Nature of the magnetic ordering -: art. no. 104404

The influence of pressure on the structure and magnetic properties of the layered hybrid compounds Cu-2(OH)(3)(n-CmH2m+1CO2).zH(2)O is investigated for m=10 and 12. It is shown that the distance between magnetic copper(II) layers, up to 40.7 Angstrom, is not significantly modified and that the temperature of the ferromagnetic ordering decreases linearly with pressure increase. We present a new analysis of the susceptibility data, based on the scaling theory of phase transitions, which clearly shows up a crossover from a high-temperature two-dimensional (2D) behavior to a 3D regime at about 30 K, around 10 K above the long-range ordering temperature. A model of quantum ferromagnetic layers interacting through dipolar coupling, taking into account the temperature dependence of correlated spin domains in a mean-field approach, allows us to explain the stabilization of a 3D order at a T-C value very close to that observed experimentally. The decrease of T-C under pressure is shown to be mainly driven by the decrease of in-plane interactions, which can be caused by small variations of the Cu-O-Cu bond angles within the layer.