QUANTUM PARAMAGNETIC FLUCTUATIONS IN RBFECL3 IN A MAGNETIC-FIELD APPLIED PERPENDICULAR TO THE ANISOTROPY AXIS

The results for experimental and theoretical studies of the spin dynam ics in the crystal of RbFeCl3 in a magnetic field up to 5.5 T applied perpendicular to the anisotropy axis are reported. The data for the ex citation spectrum collected in the inelastic neutron-scattering experi ment at 5.5 K, i.e., well above the phase-transition temperature, are treated in accordance with the theory developed for the quantum parama gnetic fluctuations in spin-1 systems with strong easy-plane-type anis otropy. Ln order to check the theory, the parameters extracted from th e spectrum evaluation are used to calculate the expected dependencies of the ratios between intensities of two measured excitation branches on momentum transfer and magnetic field. No additional fitting paramet ers are needed to obtain a satisfactory agreement with the experimenta l ratios.