THE INFLUENCE OF MAGNETIC ORDER IN QUASI-2D ORGANIC CONDUCTORS

We report extensive magnetoresistance (MR) measurements on the charge transfer salts beta''-(ET)2AuBr2 and alpha-(ET)2KHg(SCN)4. Our results indicate that spin-density wave (SDW) groundstates in both of these m aterials modify the Fermi surfaces calculated from room temperature cr ystal parameters. In the case of beta''-(ET)2AuBr2, the shapes, sizes and orientations of three individual closed two-dimensional (2D) Fermi surface pockets have been deduced at 500 mK. The SDW groundstate in a lpha-(ET)2KHg(SCN)4 leads to the observation of a resistive ''kink'' t ransition at approximately 22 T. MR measurements made as a function of crystal orientation and temperature both above and below this ''kink' ', allow a qualitative assessment of the change in band structure at t he ''kink'' to be made.