  Neutron scattering is used to investigate spin correlations in ultra pure
single crystals of the S=1 triangular lattice NiGa2S4. Despite a Curie-Weiss
temperature of Theta_CW=-80(2) K, static (tau > 1 ns) short range (xi_ab=26(3)
\AA) incommensurate order prevails for T>1.5 K. The incommensurate modulation
Q_0=(0.155(3),0.155(3),0), Theta_CW, and the spin wave velocity (c=4400 m/s)
can be accounted for by antiferromagnetic third-nearest neighbor interactions
J_3=2.8(6) meV and ferromagnetic nearest neighbor coupling J_1=-0.35(9) J_3.
Inter-plane correlations are limited to nearest neighbors and weakened by an
in-plane field. These observations show that the short range ordered glassy
phase that has been observed in a number of highly degenerate systems, can
persist near the clean limit.
