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Summary form only given. We studied the Fermi surface of the organic conductor (TMTSF)/sub 2/NO/sub 3/ through the measurements of magnetic quantum oscillations. Two different families of oscillations are observed. Well defined Shuvnikov-de Haas(SdH) oscillations with frequency of ca. 60T can be observed below 8K and above 6T at the ambient pressure. The higher frequency oscillations reported elsewhere is not visible be low 12T. The angular magnetoresistance does not show any structure neither at Yamaji's magic angles nor at Lebed's resonance condition. Only the SdH oscillations for the field scaled by Cos /spl theta/ are added and easily separated. Under a pressure of 10kbar, different oscillations with frequency of ca. 200T is observed above 10T at 450mK. Even though it is the same frequency as so called rapid oscillations observed in other Bechgaard salts, angular dependence of oscillation frequency does not follow the simple cosine law contrary to that of (TMTSF)/sub 2/CIO/sub 4/. The amplitude of oscillations depend very oddly with sample orientation, too. Both suggest that the electron structure at low temperature is strongly modified upon application of pressure which may explain the absence of superconductivity and the field-induced spin-density waves. The angular magnetoresistance shows actually three maxima at angles which are not determined from the known theories.

Summary form only given. We report a study of the transverse magnetoresistance of the organic conductor (TMTSF)/sub 2/NO/sub 3/ at ambient pressure, in fields up to 37T and in the temperature range from 2 to 77K. For field along the lowest conductivity axis (c/sup */), two series of quantum oscillations, with temperature independent frequencies of 63T and 247T respectively, are observed in the 2-10K temperature range. The oscillations amplitude of both series decreases when the temperature departs from nearby 4K. Both series are connected to the SDW transition but cannot be accounted for by SdH model. The data is tentatively interpreted, in this temperature range, within the framework of magnetic breakthrough and quantum interferences. The anisotropy of these oscillations is also studied at 4.2K. On the other hand, the magnetic field is found to increase the SDW transition temperature, in agreement with theoretical predictions for SDW phase with imperfect nesting.

Summary form only given. We present preliminary data on the low temperature magnetoresistance of (TMTSF)/sub 2/AsF/sub 6/, investigated in a high magnetic field of 37T at liquid helium temperature in the ambient pressure spin density wave state of the compound. Starting around 15T a single series of fast oscillations periodic in I/B is visible with a fundamental frequency very close to 200T. The AsF/sub 6/ salt is believed to have physical properties very similar to those of PF/sub 6/. However this frequency is substantially lower than the 230T measured in PF/sub 6/. More detailed experiments concerning the angular and temperature dependence of both oscillatory and background magnetoresistance are in progress.