Abstract
A classical effective Hamiltonian for the quantum easy-plane ferromagnetic chain with an in-plane applied field is introduced by means of a path-integral variational method. It then becomes possible to include quantum effects of the out-of-plane fluctuations in an easily evaluable phase-space integral which approximates the quantum partition function. A comparison with experimental data for the excess specific heat of shows much improvement in the description of this system. In addition, new light is shed on the old problem of defining the classical counterpart of a spin Hamiltonian.
- Received 25 March 1991
DOI:https://doi.org/10.1103/PhysRevB.44.903
©1991 American Physical Society