Study of the anomalous behaviour in the susceptibility of the quasi-2D quantum Heisenberg antiferromagnetic model

We investigate the temperature dependence of the longitudinal susceptibility of a quantum spin- 1/2 Heisenberg antiferromagnetic model as a function of the magnetic field and interplane exchange interaction J ′ = λ J on a simple cubic lattice. We use the famework of the effective-field theory with correlation. It is shown that for very weak interplane coupling ( λ < 1 0 − 5 ) and high-field ( H / J > 2.0 ) an anomalous behaviour is observed in accordance with experimental results for the compound La2CuO4. We also discuss the origin of this anomaly, which is not observed in the quasi-2d Ising and the classical Heisenberg models.