Ordering and Excitations in the Field-Induced Magnetic Phase of   Cs_3Cr_2Br_9
  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. 
B. Grenier, Y. Inagaki, L.P. Regnault, A. Wildes, T. Asano, Y. Ajiro,   E. Lhotel, C. Paulsen, T. Ziman and J.P. Boucher