ELECTRON-SPIN ECHO AND EPR STUDIES OF PARAMAGNETIC CENTERS IN POLYCRYSTALLINE C-60

Three different paramagnetic centers were detected by X-band EPR in C6 0 powder sample below 60 K and identified as C60+ radical (g=2.0028), dimers of C60+ radicals with zero field splitting D=0.00054 cm-1, and conducting electrons (g=2.0021) of graphite residuals. Only C60+ EPR s ignals persist at room temperature and all spectral lines saturate eas ily for microwave powers higher than 50 mW. Two spin-lattice relaxatio n time T1 and two phase memory times T(M) describe the system with T1= 500 mus and T(M)=2.6 mus for C60+ at 20 K. An anomaly in T1 and T(M) i s observed at about 55 K where the field-swept ESE spectrum is narrowe st and where the anomaly in the dielectric permittivity is observed. I t indicates an existence of a phase transition in this temperature ran ge.