Effect of cotunneling and spin polarization on the large tunneling magnetoresistance effect in granular C-Co films

グラニュラーC-Co薄膜の巨大TMR効果におけるコトンネリングとスピン偏極の効果

境 誠司; 三谷 誠司*; 菅井 勇; 高梨 弘毅; 松本 吉弘; 圓谷 志郎; 楢本 洋*; Avramov, P.; 前田 佳均

Sakai, Seiji; Mitani, Seiji*; Sugai, Isamu; Takanashi, Koki; Matsumoto, Yoshihiro; Entani, Shiro; Naramoto, Hiroshi*; Avramov, P.; Maeda, Yoshihito

Magnetotransport properties of the granular C-Co films are investigated over the broad bias voltage range from the region near zero bias by using the samples with the CPP (current-perpendicular-to-plane) geometry. It is revealed that the granular C-Co films show the I-V characteristics ascribed to cotunneling whose magnitudes are comparable to other molecular-based granular films. Furthermore, by considering the contribution of cotunneling on the magnitude of the TMR effect, it is successfully demonstrated that the tunnelling electrons generated at the interface between Co nanoparticles and a C-based matrix (C-Co compound) in the films have a significantly higher spin polarization (50-80%) than those in Co crystal and at the Al-oxide/Co interface. The present results clearly suggest that the high interfacial spin polarization is the most important cause of the large TMR effect in the granular C-Co films, in spite of the cotunneling-induced enhancement.