  Field-induced magnetic order has been investigated in detail in the
interacting spin 3/2 dimer system Cs_3Cr_2Br_9. Elastic and inelastic neutron
scattering measurements were performed up to H = 6 T, well above the critical
field H_c1 = 1.5 T. The ordering displays incommensurabilities and a large
hysteresis before a commensurate structure is reached. This structure is fully
determined. Surprisingly, the lowest excitation branch never closes. Above
H_c1, the gap increases slowly with field. An analysis in terms of projected
pseudo-spin is given.
