Quantum Monte Carlo Investigation of the magnetic properties of weakly interacting antiferromagnetic chains with an alternating exchange interaction with spin S = 1/2

Abstract

An approximation dependence of the spontaneous magnetic moment at a site, σ/σ(0) − 1 = and the antiferromagnet-singlet state phase boundary, J2/J1 = 0.52(3)δ, are determined by the quantum Monte Carlo method in the self-consistent sublattice molecular field approximation for weakly inter-acting (J2) antiferromagnetic chains with spin S = 1/2 and alternating exchange interaction (J1 ± δ). The Neel temperature and a number of critical temperatures which could be related with the filling energy of two singlets (ΔSz = 0) and one triplet (ΔSz = 1) spin bands, each of which is split by the sublattice field (hx, y ≠ hz into two subbands, are determined on the basis of the computed correlation radii of the two-and four-spin correlation function, the squared total spin 〈 (Sz)2〉 with respect to the longitudinal components, the dimerization parameter, and the correlation functions between the nearest neighbors with respect to longitudinal and transverse spin components. On the basis of the Monte Carlo calculations, the critical temperatures and possible energy gaps at the band center are determined for the antiferromagnets CuWO4 and Bi2CuO4 and for the singlet compounds (VO)2P2O7 and CuGeO3, agreeing satisfactorily with existing results, and new effects are also predicted.