Abstract
Using a combination of high-temperature series expansion, exact diagonalization, and quantum Monte Carlo, we perform a complementary analysis of the thermodynamic properties of quasi-one-dimensional mixed-spin systems with alternating magnetic moments. In addition to explicit series expansions for small spin quantum numbers, we present an expansion that allows a direct evaluation of the series coefficients as a function of spin quantum numbers. Due to the presence of excitations of both acoustic and optical nature, the specific heat of a mixed-spin chain displays a double-peak-like structure, which is more pronounced for ferromagnetic than for antiferromagnetic intrachain exchange. We link these results to an analytically solvable half-classical limit. Finally, we extend our series expansion to incorporate the single-ion anisotropies relevant for the molecular mixed-spin ferromagnetic chain material with alternating spins of magnitude 5/2 and 1. Including a weak interchain coupling, we show that the observed susceptibility allows for an excellent fit and the extraction of microscopic exchange parameters.
- Received 31 July 2003
DOI:https://doi.org/10.1103/PhysRevB.69.174430
©2004 American Physical Society