Selfconsistently renormalized spin-wave approximation for some two-dimensional magnetic systems

Some temperature-dependent properties of two-dimensional magnetic hamiltonians with uniaxial anisotropy are studied on the basis of the selfconsistently renormalized (SCR) spin-wave approximation. Due to the importance of anisotropy in two- dimensional systems, particular attention is paid to the kinematical consistency of the theory by considering multiple scattering due to anisotropy. In particular the properties of FeCl 2 , a layer ferromagnet with large single-ion and exchange anisotropy, and K 2 NiF 4 , a layer antiferromagnet with small anisotropy have been studied. In both cases good agreement with experiments is found for temperature renormalization of small k spin-wave energies. Improved results with respect to spin-wave theory are obtained for the order parameter. The large k dependence in the temperature renormalization of spin-wave energies is predicted for antiferromagnets with medium and small anisotropy.