Field-induced anisotropy crossover in copper pyrazine perchlorate Cu(pz)$_{2}$(ClO$_{4}$)$_{2}$

The temperature-dependent magnetization of a single crystal of the 2D QHAF copper pyrazine perchlorate was studied at different fields along all three crystalline orientations. The crystal has identical response when the applied field lies within the layer, only showing a low temperature minimum for fields larger than 3 kOe. The temperature of the minimum increases smoothly with the field strength. The effect is explained as a field-induced 2D Heisenberg to 2D XY anisotropy crossover [1]. \newline \newline [1] A. Cuccoli et al, Phys. Rev. B \textbf{68}, 060402 (2003).