Temperature dependence of electron spin resonance and electrical conductivity in P+-implanted C60 films and their derivatives

Abstract

The temperature dependence of electron spin resonance ͑ESR͒ has been measured to clarify the origin and nature of paramagnetic states responsible for the observed ESR signal in P ϩ -implanted C 60 films. Also, the temperature dependence of electrical conductivity was made and compared with ESR linewidths to detect the transport mechanism in these films. The ESR experiments were performed at 9.4 GHz in a wide temperature range from 3.7 to 300 K. The temperature dependence of the ESR signal intensity and spin susceptibility revealed that the unpaired spin follows the Curie law at TϽ20 K, while a clear deviation was observed at TϾ20 K. The Curie behavior of the spin susceptibility results from localized dangling bond electrons, while a deviation occurs due to delocalization and excitation of electrons into states as the temperature increases. The temperature dependence of linewidths indicates that the spin mobility occurs by hopping, taking into account that the electron-phonon interaction as spin relaxation mechanism at TϾT min . The observed minimum in linewidths can be attributed to a decrease in the narrowing effects as the temperature decreases. Finally, the temperature dependence of the electrical conductivity and ESR resonance signal linewidth suggests that the transport mechanism occurs by hopping motion and the unpaired spins are partially localized.