Double-layer antiferromagnetic quantum spin-1/2 Heisenberg model: study of the ground state

The crossover from two-dimensional to three-dimensional behavior in the quasi-two-dimensional quantum Heisenberg antiferromagnetic model in the presence of a magnetic field, at T=0 (ground state), is studied by using effective-field theory. In the model a nearest neighbour spin pair interacts with strength J in the xy-plane and with λJ (0⩽λ⩽1) in the z-axis. The critical field Hc is obtained as a function of parameter λ, where we have different values of the classical case (Ising model) Hc/J=4+2λ.