SPIN-WAVE THEORY FOR A FRUSTRATED ANTIFERROMAGNETIC HEISENBERG-MODEL ON A SQUARE LATTICE

A spin wave theory for a frustrated antiferromagnetic Heisenberg model on a square lattice is developed using spin operators introduced by Oguchi and Honma. Exchange integrals between nearest neighbor and next nearest neighbor are denoted by J1=pJ and J2=(1-p)J where 0≦p≦1, and J is a positive constant. Since the ground state for 0≦p≦1/3 is different from that for 1/3≦p≦1, they are treated separately. The energy, staggered magnetization and correlation functions in the ground state are calculated over the whole range of p. For the special case of p = 0, they are compared with Takahashi's theory. Furthermore, direct calculations for finite lattice with 16 and 20 spins are shown for reference. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.