Spin-Wave Dispersion in KMnF3

The spin-wave dispersion curve of antiferromagnetic KMnF3 at 4.2°K has been measured by means of neutron inelastic scattering. With incident neutron energies of 105° and 165°K, propagation was observed out to the zone boundary in the pseudocubic (110) plane. Least-squares fitting of the spin-wave energies to an expression involving the nearest and next-nearest-neighbor exchange interactions J1 and J2 and an anisotropy field HA yielded the results J1/k=3.80°±0.04°K, J2/k=0.11°±0.02°K and HA=3.1±0.4 kOe.