Thermodynamics of alternating quantum [formula omitted] chains with z-z type couplings and local uniaxial anisotropy on quantum spins S′

Abstract

We examine the case of ferrimagnetic chains made up of two sublattices ( 1 2 , s′) , characterized by z-z exchange couplings between nearest neighbors and a z-uniaxial anisotropy on the quantum spins s′ s′ ⩽ 5 2 ) . We use the transfer-matrix method for obtaining closed-form expressions of the partition function and its derivatives with respect to the applied field, when this last one is parallel to the z-axis of quantization. We mainly focus on the low-temperature behavior of the parallel susceptibility χ ∥. In the low-temperature range, the chain can be considered as an assembly of quasi-independent quasi-rigid blocks, each one with length ξ, the correlation length. Then we specifically focus on the case of a compensated chain and, at T= 0 K, we build up a ‘map’ of the ξ ∥ T behavior as function of k z / J (where J i s the exchange energy and k z the anisotropy cosntant).