Coherent-Anomaly Method Applied to the Quantum Heisenberg Model

The coherent-anomaly method proposed by M. Suzuki is applied to the spin 1/2 ferromagnetic Heisenberg model to estimate the critical exponents. The effective Hamiltonian method to small-sized clusters for the simple cubic lattice, and the inverse temperature power series expansion of the susceptibility for the face centered cubic lattice are combined with the CAM. Both results show that the CAM is useful for the quantum spin systems.