  We report the results of neutron scattering on a powder sample of Gd3Ga5O12
at high magnetic fields. We find that in high fields (B>1.8 T) the system is
not fully polarized, but has a small canting of the moments induced by the
dipolar interaction. We show that the degree of canting is accurately predicted
by the standard Hamiltonian which includes the dipolar interaction. The
inelastic scattering is dominated at large momentum transfers by a band of
almost dispersionless excitations. We show that these correspond to the spin
waves localized on ten site rings, expected for a system described by a nearest
neighbor interaction, and that the spectrum at high fields B>1.8 T is
well-described by a spin wave theory. The phase for fields <1.8 T is
characterized by an antiferromagnetic Bragg peak at (210) and an incommensurate
peak.
