HIGH-FIELD MAGNETOTRANSPORT STUDIES OF BETA''-(BEDT-TTF)2AUBR2

We have measured the high-field magnetoresistance (MR) of the quasi-tw o-dimensional organic metal beta''-ET2AuBr2 over a wide range of angle s and temperatures. Band structure calculations using the overlaps of Mori et al. yield a Fermi surface (FS) consisting of an open section a nd only a single closed hole pocket [1] for this material. However, Sh ubnikov-de Haas (SdH) frequencies are observed in the MR with fundamen tal fields of 39 T, 141 T, 180 T and 219 T plus harmonics, and so a de tailed study or the temperature and angle dependence of the amplitude of the SdH oscillations was carried out in order to clarify the origin of the different frequencies. We propose the existence of a 2c spin d ensity wave modulation driven by the nesting properties of the open se ction of the FS, and interpret the different SdH frequencies in terms of the modified band structure and the Shoenberg magnetic interaction.