Quantum Fluctuations in the Frustrated Antiferromagnet Sr2Cu3O4Cl2

Sr2Cu3O4Cl2 is an antiferromagnet consisting of weakly coupled CuO planes which comprise two weakly interacting antiferromagnetic subsystems I and II which order at respective temperatures TI≈390 K and TII≈40 K. Except asymptotically near the ordering temperature, these systems are good representations of the two-dimensional quantum spin-1/2 Heisenberg model. For T