Field-Induced 2D XY behavior in Molecular-Based Antiferromagnets

Two-dimensional XY behavior has long been observed in layered superfluids and superconductors but has never convincingly been detected in magnetic materials. Recent theoretical work$^{1}$ predicts that an external field can cause a well-isolated 2D Heisenberg antiferromagnet to crossover to 2D XY behavior at low temperatures, with characteristic behavior in the magnetization and specific heat. We report on the field-dependent magnetization M(H,T) of Cu(pz)$_{2}$(ClO$_{4})_{2}$ (pz = pyrazine), a well-isolated, molecular-based S=1/2 Heisenberg antiferromagnet (J/k = 17 K), with behavior strongly resembling that predicted by Cuccoli. $^{1}$ A. Cuccoli et al, Phys. Rev. B vol. 68, 060402 (2003).