Thermodynamic properties of an alternating-spin (1/2,1) two-leg ladder

With the aid of the Schwinger-boson mean-field method, we study the low-lying excitations and thermodynamic properties of a ferrimagnetic Heisenberg two-leg ladder (i.e., a ferrimagnetic double-chain with an antiferromagnetic interaction). The interaction between the two chains plays an important role in producing a low-lying excitation energy gap, affecting the low-lying excited spectrum, and increasing the disorder of the ferrimagnetic double-chain. The excitation spectrum, energy gap, and spin reduction in the ground state are calculated. Thermodynamic quantities such as the short-range spin correlation and short-range order are also obtained at low temperatures. In this gapful system, we observed the exponential behaviors in both the specific heat (C <Subscript> V </Subscript>) and the product of magnetic susceptibility and temperature (χT) at low temperatures. The exponential behavior of the χT versus temperature agrees qualitatively with the experimental results in NiCu(pba)(D<Superscript>2</Superscript>O)<Superscript>3</Superscript> · D<Superscript>2</Superscript>O at low temperatures. Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2004