  Spin wave dispersion in the frustrated fcc type-III antiferromagnet MnS$_2$
has been determined by inelastic neutron scattering using a triple-axis
spectrometer. Existence of multiple spin wave branches, with significant
separation between high-energy and low-energy modes highlighting the intrinsic
magnetic frustration effect on the fcc lattice, is explained in terms of a spin
wave analysis carried out for the antiferromagnetic Heisenberg model for this
$S=5/2$ system with nearest and next-nearest-neighbor exchange interactions.
Comparison of the calculated dispersion with spin wave measurement also reveals
small suppression of magnetic frustration resulting from reduced exchange
interaction between frustrated spins, possibly arising from anisotropic
deformation of the cubic structure.
