THEORETICAL CALCULATION OF THE MAGNETIC PROPERTIES IN DISORDERED GROUND STATE FOR SPIN-1/2 ANTIFERROMAGNET
DU ANa, WEI GUO-ZHUb
a College of Sciences, Northeastern University, Shenyang 110006, China; b International Centre for Materials Physics, Academia Sinica, Shenyang 110015, China, and College of Sciences, Northeastern University, Shenyang 110006, China
Abstract 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 λ'J, and in xy plane it is 2 λJ. In bond-operator representation, within the mean-field decoupling approximation, we have calculated the phase diagram for order-disorder phase transition about λ and λ' at 0 K, obtained the critical value, λc=0.292, within which the disordered phase is stable in two-dimensional case(λ'=0), and found that the disordered phase is always stable for λ'<1 in one-dimensional case(λ=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 λ and λ'.
Received: 05 February 1996
Published: 20 March 1997
(Quantized spin models, including quantum spin frustration)