Neutron scattering measurement of spin-wave dispersion in Rb2CrCl4: a two-dimensional easy-plane ferromagnet

Abstract
The spin-wave dispersion relations for Rb2CrCl4, which orders ferromagnetically at 63K have been measured at 4.5K. The spin-wave energies confirm the two-dimensional nature of the interactions; writing H12=-2J12S1.S2 they can be fitted by a single exchange parameter J1=0.66+or-0.01 meV (7.7+or-0.1K) representing the interaction between nearest-neighbour in-plane ions. Rb2CrCl4 should therefore typify a two-dimensional, S=2, easy-plane ferromagnet.