THEORETICAL CALCULATION OF THE MAGNETIC PROPERTIES IN DISORDERED GROUND STATE FOR SPIN-1/2 ANTIFERROMAGNET

The spin-1/2 quantum antiferromagnet in three-dimensional space can be described by Heisenberg model:two nearest-neighbor spins with strong interaction in z direction consistitute a dimer, every dimer can be considered as a lattice site in the tetragonal lattice. In z direction, the exchange interaction between two nearest-neighbor dimers is \lambda 'J, and in xy plane it is 2\lambdaJ. In bond-operator representation, within the mean-field decoupling approximation, we have calculated the phase diagram for order-disorder phase transition about \lambda and \lambda ' at 0 K, obtained the critical value, \lambda_c = 0.292, within which the disordered phase is stable in two-dimensional case(\lambda = 0), and found that the disordered phase is always stable for \lambda'<1 in one-dimensional case(\lambda = 0). For the disordered phase, the physical quantities, such as energy gap, ground-state energy, two-point correlation functions and correlation lengths in xy plane and in z direction, have been calculated as functions of parameters \lambda and \lambda'.