Spin-wave theory of the nearly two-dimensional ferromagnet (C 3H 7NH 3) 2CuCl 4

Abstract

A renormalized spin-wave theory is developed for the layer-type ferromagnet (C 3H 7NH 3) 2CuCl 4. In contrast with the case of K 2CuF 4, the main perturbation to the isotropic intralayer exchange interaction leading to three-dimensional long-range order is here the anisotropy in the intraplanar interaction. An analytical expression for the magnetization of the two-dimensional Heisenberg ferromagnet with a weak anisotropy in the intraplanar exchange as well as interplanar interactions has been obtained. It is shown that an excellent agreement between theory and experiment can be obtained using the interaction constants estimated in previous investigations, and further that the spin-wave interactions have a significant effect on the temperature dependence of the magnetization.