LOW-TEMPERATURE ASYMPTOTICS OF ISOTROPIC FERROMAGNETIC CHAINS AT NONZERO FIELDS

We derive the leading-order asymptotics of classical one-dimensional i sotropic ferromagnets near zero temperature in the context of two mode ls with short-range interactions, namely the Heisenberg and the logari thmic chain. It is shown that the thermodynamics, in both cases, asymp totically reduce to the same differential equation, which also describ es the azimuthally symmetric quantum motion of a rigid rotator in an e xternal field. The result reflects the deep-rooted analogy between the rmal and quantum fluctuations in classical d-dimensional and quantum ( d-1)-dimensional systems, respectively. Explicit analytical expression s given in the limiting cases of high and low fields agree with the fu ll numerical solution to within a few percent.