The high temperature expansion of the classical XYZ chain

Abstract

We present the β-expansion of the Helmholtz free energy of the classical XY Z model, with a singleion anisotropy term and in the presence of an external magnetic field, up to order β 12 . We compare our results to the numerical solution of Joyce's [Phys. Rev. Lett. 19, 581 (1967)] expression for the thermodynamics of the XXZ classical model, with neither single-ion anisotropy term nor external magnetic field. This comparison shows that the derived analytical expansion is valid for intermediate temperatures such as kT /Jx ≈ 0.5. We show that the specific heat and magnetic susceptibility of the spin-2 antiferromagnetic chain can be approximated by their respective classical results, up to kT /J ≈ 0.8, within an error of 2.5%. In the absence of an external magnetic field, the ferromagnetic and antiferromagnetic chains have the same classical Helmholtz free energy. We show how this two types of media react to the presence of an external magnetic field.

Thermodynamics of the Mn12-ac molecule in a skew magnetic field at T \gtrsim 21 K

“…A good approximation for the HFE of the quantum and classical versions of the Mn 12 -ac crystals for T 46 K, except for the calculation of the transverse component of the magnetization, is obtained by substituting the parameters (14) in expansions (A.1) and (B.4) and taking C = 0 and E = 0. The expansion of the HFE of the quantum model of Mn 12 -ac, up to order O(T −3 ), is…”