THERMODYNAMICS OF ALTERNATING (S,S') CHAINS IN THE NEAREST-NEIGHBOR ISING-MODEL APPROXIMATION

The exact solutions of the so-called (1/2,s')N ferrimagnetic z-z chain made up of two sublattices have been previously derived by using the transfer-matrix method. In this paper, we generalize this method to (s,s')N chains, with arbitrary s and s'. We give a general expression for the correlation length-xi and the product chi(parallel-to)T in the low-temperature range. We specifically discuss the case of the moment-compensated chain in the low-temperature limit and generalize the results previously obtained. We show that, in this limit, the chain behaves as an assembly of quasi-independent, quasirigid blocks, each with length-xi, and that, in the low-temperature range, the product chi(parallel-to)T behaves as xi-M2, with M the thermal-average magnitude of the magnetic moment attributed to the unit cell.