A Neutron Scattering Study of the H-T Phase Diagram of the Bond   Frustrated ZnCr2S4
  Detailed neutron scattering measurements on the bond frustrated magnet ZnCr2S4 reveal a rich H-T phase diagram. The field dependence of the two subsequent antiferromagnetic transitions follows closely that of recently reported structural instabilities, providing further evidence for spin driven Jahn-Teller physics. The incommensurate helical ordered phase below TN1 = 15.5 K exhibits gapless spin wave excitations, whereas a spin wave gap (about 2 meV) opens below TN2 = 8 K as the system undergoes a first-order transition to a commensurate collinear ordered phase. The spin wave gap is closed by a strong magnetic field. 
D. Hsieh, Y. W. Li, S. Watauchi, Chang Liu, Q. Huang, R. J. Cava, J.   W. Lynn and M. Z. Hasan
cond-mat.str-el