IDENTIFICATION OF DIFFERENT MAGNETIC-MODES IN CSFECL3 BY POLARIZATIONANALYSIS

CsFeCl3 is a quasi-one-dimensional (1D) magnetic system with a singlet ground state. The Fe2+ ion has an effective spin S = 1. Experimental results in a magnetic field applied perpendicular to the anisotropy ax is show that the excited states (doubly degenerate in zero field) spli t and shift to higher frequencies with increasing field. The splitting of the high-frequency modes is very small compared to the instrumenta l resolution. Only polarisation analysis of inelastic neutron scatteri ng made it possible to observe the splitting everywhere in reciprocal space. The frequency shift of the two modes with field is different su ch that a mode crossing appears for fields below about 4 T.