High spin polarization at the Fe/C60 interface in the Fe-doped C60 film

A process of tunneling conduction and the spin-dependent resistivity change (so-called tunneling magnetoresistance effect) in the Fe-doped C60 film with a granular structure is investigated for the current-into-plane device. Cooperative tunneling (cotunneling) through several Fe nanoparticles is suggested to be operative at temperatures lower than 20 K. By considering the effect of cotunneling on the magnetoresistance ratio, it is successfully shown that the spin polarization of tunneling electrons generated at the Fe/C60 interface is much higher than that in Fe crystal at low temperature in a similar fashion to that at the Co/C60 interface in the Co-doped C60 films. A strong temperature dependence of spin polarization is observed, suggesting a possible influence by the thermally induced disorders ascribed to the Fe atoms bonded with C60 in the C60Fe compound.