arXiv:cond-mat/0510441 · Physical Review B
High-temperature series expansion of the Helmholtz free energy of the quantum spin- S XYZ chain
Onofre Rojas, S. M. de Souza, E. V. Corrêa Silva, M. T. Thomaz
Abstract
We consider the $XYZ$ chain model of arbitrary spin $S$ in the high-temperature region, with external magnetic field and single-ion anisotropy term. Our high-temperature expansion of the Helmholtz free energy is analytic in the parameters of the model for $S$, which may range from $1∕2$ to the classical limit of infinite spin $(S\ensuremath{\rightarrow}\ensuremath{\infty})$. Our expansion is carried out up to order ${(J\ensuremath{\beta})}^{5}$. Our results agree with numerical results of the specific heat per site for $S=1∕2$, obtained by the Bethe ansatz, with $h=0$ and $D=0$. Finally, we show that the magnetic susceptibility and magnetization of the quantum model can be well approximated by their classical analog in this region of temperature.