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.
Ground‐state properties for an easy‐plane spin‐one ferromagnet: The coupled‐cluster method
In this paper we have investigated the ground state of an easy‐plane spin‐one ferromagnet: H = D∑i(Sxi)2 −(J/2)∑(i, j)Si⋅Sj −h∑iSzi, using the coupled‐cluster method. The mean‐field approximation is commonly used in calculations of thermodynamic quantities for such systems because of the complexities caused by the single‐ion anisotropy term. However, in the mean‐field approximation both quantum and spin fluctuation correlations are neglected. Above the critical point, the zero‐temperature series expansion method has been used to obtain estimates of the critical crystal field potential (Dc) and critical exponent of the susceptibility. Using the coupled‐cluster method we obtained the ground‐state energy, magnetization and critical point for both two‐ and three‐dimensional lattices.
Spin waves in terbium. III. Magnetic anisotropy at zero wave vector
The energy gap at zero wave vector in the spin-wave dispersion relation of ferromagnetic. Tb has been studied by inelastic neutron scattering. The energy was measured as a function of temperature and applied magnetic field, and the dynamic anisotropy parameters were deduced from the results. The axial anisotropy is found to depend sensitively on the orientation of the magnetic moments in the basal plane. This behavior is shown to be a convincing indication of considerable two-ion contributions to the magnetic anisotropy at zero wave vector. With the exception of the sixfold basal-plane anisotropy of the unstrained lattice, the dynamic anisotropy parameters deduced from our results agree with macroscopic measurements both with respect to the magnitudes (at zero temperature) and the temperature dependences. The deviations observed cannot be explained by existing theories which include the effects of zero-point deviations from the fully aligned ground state, and we tentatively propose polarization-dependent two-ion couplings as their origin.