Pair dynamical correlated-effective-field approximation

The dynamical correlated-effective-field approximation (DCEFA) developed by Suzuki is extended to the pair-approximation, in which the spin-pair is solved exactly and the interaction between the pairs is treated by the DCEFA. The approximation is applied to calculate magnetic excitation and uniform static susceptibility of S = 1/2 exchange-alternating chains. The obtained results agree reasonably well with those obtained by the exact diagonalization method for finite spins. The approximation is applied also to real pseudo-one-dimensional antiferromagnetic-ferromagnetic alternating systems such as Cu(TIM)CuCl4, (4-BzpipdH)CuCl3 and MeNN, and the exchange couplings including interchain coupling in these systems are evaluated.