High interface spin polarization and its mechanism in fullerene-magnetic metal systems

Sakai, Seiji; Mitani, Seiji*; Matsumoto, Yoshihiro; Otomo, Manabu; Entani, Shiro; Avramov, P.; Naramoto, Hiroshi*; Fujikawa, Takashi*

Voltage-dependence of the TMR effect was investigated for the granular C-Co films. It was successfully demonstrated that the large TMR is attributed to the very high spin polarization of tunnelling electrons at the C-Co compound/Co interface. In order to study the mechanism of the spin polarization, the electronic and magnetic states of the C-Co compound at the interface with magnetic metals (Ni) were investigated by the X-ray magnetic circular dichroism (XMCD) spectroscopy. It was revealed that the region of the C-Co compound within 3 nm from the interface is ferromagnetically coupled with Ni due to the indirect exchange interaction mediated by C. This ferromagnetic coupling is able to give rise to the high spin polarization in connection with the spin-filtering effect of the C-Co compound.