Effects of coupling between chains on the magnetic excitation spectrum of KCuF3.

Abstract

The effects of the small ferromagnetic coupling between chains on the dynamical behavior of the spins in ${\mathrm{KCuF}}_{3}$ are investigated. Inelastic neutron-scattering measurements of the magnetic excitations in ${\mathrm{KCuF}}_{3}$ were made using a triple-axis spectrometer. The scattering was studied at a number of temperatures; measurements below ${\mathit{T}}_{\mathit{N}}$=39.07\ifmmode\pm\else\textpm\fi{}0.02 K showed well-defined spin waves for energies less than the interchain zone-boundary energy of 11.5 meV. At higher energies a continuum of scattering was observed. The measurements are compared with spin-wave theory, and the field theory used in the preceding paper (paper I). At a temperature of 9 K the scattering at energy transfers of 25 meV and below are in excellent agreement with spin-wave theory when two-magnon processes are included. Above the N\'eel ordering temperature the measurements are compared with field theory. Although this qualitatively describes the temperature behavior of the line shapes it does not account for the observed change in intensity with temperature. This discrepancy is explained by residual interchain correlations.