An extension of the characteristic angle method to the easy-plane spin-32 ferromagnet
Abstract The characteristic angle (CA) method [J. Phys. A 27 (1994) 5599], developed previously for the easy-plane spin-1 magnetic systems, has been successfully extended to the spin - 3 2 case. A compact form of the CA spin - 3 2 operator transformation is given. Then the ground state energy, the magnon dispersion relation and the spontaneous magnetization are discussed for an easy-plane spin - 3 2 ferromagnet by using the CA method. A comparison with the old theoretical methods is made.
Canonical transform theory of spin‐waves in strongly anisotropic magnets
We have developed a new infinite‐order perturbation approach for treating strongly anisotropic magnets. This formalism is based on a canonical transformation of a given system into a new system with an effective two‐ion anisotropy which, for example, can be treated by conventional spin‐wave techniques. An expression for the spin‐wave energy for the general conical magnetic moment configuration with arbitrary single‐ion anisotropy has been derived using this formalism. It was found that an analysis of the transverse spin‐wave spectra can at most result in a determination of a renormalized exchange integral and two renormalized anisotropy constants. A comparison of the theoretical predictions of this formalism with experimentally determined spin‐wave spectra indicate that a substantial part of the large two‐ion anisotropy, which had been previously introduced to describe the spin‐wave spectra in the heavy rare earth series, actually resulted from the fitting procedure which was used and not from any physica...
Zero-temperature properties of quantum spin systems in two dimensions
We consider the zero-temperature properties of four different spin 1/2 models on two-dimensional lattices: the XY ferromagnet, the XY antiferromagnet, the Heisenberg antiferromagnet, and the Dzyaloshinsky–Moriya models. Most of this article is a review of previously published work, but a few previously unpublished results are included. The relation between three of the models on bipartite lattices is described. The properties of the XY ferromagnet in two dimensions, especially those derived from extrapolation of finite lattice results, are reviewed. A numerical factor by which spin-wave and finite-lattice estimates of the long-range order parameter differ is discussed. For frustrated models on the triangular lattice the possibility of a chirality phase transition instead of, or in addition to, a magnetic phase transition is considered.