EN
Different intercalated carbon systems: K_xC_{60}, Rb_xC_{60} as well as highly oriented pyrolytic graphite + potassium with unstable structural and superconducting behavior were investigated with the EPR and magnetically modulated microwave absorption techniques. Three characteristic, well-separated EPR signals were observed for A_xC_{60} (A = K or Rb) systems at the early stages of doping process. We ascribed these signals to C_{60}^+, C_{60}^{1-}, and C_{60}^{3-} radicals. Evolution of the EPR spectrum characterizes different phases of K_xC_{60} system including superconducting one. Two superconducting phases with T_c^{(1)}=(21±0.5) K (unstable) and T_c^{(2)}=(18.5±0.5) K (final, stable) were distinctly separated for K_xC_{60} system. For C_{60} intercalated by rubidium a similar evolution of EPR spectrum is observed. Prior to well-defined superconducting Rb_3C_{60} phase was created, strong instabilities of the magnetically modulated microwave absorption signal were observed at the narrow part of the doping process. For potassium intercalated highly oriented pyrolytic graphite, EPR oscillations below 100 K were observed as well as Josephson hysteresis loops were registered at 5 K.