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Highly spin-polarized tunnel magnetoresistance in granular C$$_{60}$$-Co films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Takanashi, Koki; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Naramoto, Hiroshi*; Maeda, Yoshihito

In the present study, we examine the bias-voltage (V) and temperature (T) dependences of the spin-dependent transport properties of the granular C$$_{60}$$-Co films (C$$_{60}$$Co$$_{6-10}$$) in the current perpendicular to plane (CPP) geometry for the origin of the large TMR effect. At low T, the CPP samples show much higher MR than the upper limit of TMR (MR = 50%) derived from the Julliere's model. From the I-V characteristics, we evaluated the degree of the higher order tunneling process, as a possible cause of the MR enhancement above MR = 50%, to be 3-7 at low temperatures, which changes depending on the sample composition and device structure. After considering this MR enhancement effect, we can evaluate the spin-polarization of the tunneling electrons generated at the C$$_{60}$$-Co compound/Co interface. The evaluated values are remarkably high, i.e., P $$>$$ 75% at zero temperature, compared to Co crystal (P = 30%).



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