Electron spin echo and EPR studies of paramagnetic centers in polycrystalline C 60

Abstract

Three different paramagnetic centers were detected by X-band EPR in C 60 powder sample below 60 K and identified as C 60 + radical ( g=2.0028), dimers of C 60 + radicals with zero field splitting D=0.00054 cm −1, and conducting electrons ( g=2.0021) of graphite residuals. Only C 60 + EPR signals persist at room temperature and all spectral lines saturate easily for microwave powers higher than 50 mW. Two spin-lattice relaxation time T 1 and two phase memory times T M describe the system with T 1=500 μs and T M=2.6 μs for C 60 + at 20 K. An anomaly in T 1 and T M is observed at about 55 K where the field-swept ESE spectrum is narrowest and where the anomaly in the dielectric permittivity is observed. It indicates an existence of a phase transition in this temperature range.