Abstract
A self-consistent cluster approximation is developed for the wave-vector ()-dependent spin-spin correlation in Ising models describing magnetic and ferroelectric systems. The method is particularly suitable for describing systems with competing short-range interactions. The selfconsistent approximation for the -dependent susceptibilities with clusters of size is found to be , , where are the eigenvalues of the Fourier transform of where is the pair-correlation matrix of spins within the cluster calculated by the exact Hamiltonian of the cluster. The constant is the ratio of the number of nearest neighbors inside the cluster to the total number of nearest neighbors. The method is applied to calculate scattering intensities in potassium-dihydrogen-phosphate-type hydrogen-bonded ferroelectrics. We find a strong anisotropy in the dependence of the intensity, exhibiting a strong suppression of fluctuations along the easy () axis. The results are found to be in good agreement with neutron scattering data in KP. We also investigate the ice-rule limit of our results. In that case a singularity of the type for is found, similar to that generated by long-range dipolar forces.
- Received 2 December 1981
DOI:https://doi.org/10.1103/PhysRevB.25.5828
©1982 American Physical Society