MAGNETO-OSCILLATORY BEHAVIOR AND MAGNETISM IN QUASI-2-DIMENSIONAL ORGANIC CONDUCTORS

We have studied the magneto-oscillatory behavior of quasi-two-dimensio nal (quasi-2D) organic conductors of the type (BEDT-TTF)2XHg(SCN)4, wh ere X = K, Rb, NH4, in order to probe the underlying magnetic behavior of these materials. The K and Rb compounds are metallic down to 50 mK , but are not superconducting. They both display a dual series of magn eto-oscillations, a magnetic ordering at low temperatures, below about 10 K, and a sharp drop in the magnetoresistance associated with the d estruction of this phase with the application of high magnetic fields at low temperatures. In contrast, the NH4 material is a superconductor at low temperatures (below 1 K) up to a pressure of at least 4 kbar. It also displays a complex background magnetoresistance upon which is superposed a single oscillation series. In all three organic materials , there is a strong interaction between the underlying magnetic phases (which influences the open orbits) and the magneto-oscillations which result from the quasi-2D Fermi surface behavior.