Giant tunnel magnetoresistance and interface spin-polarization in granular C60-Co films

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

We investigated the bias-voltage (V) and temperature (T) dependences of the spin-dependent transport properties of the granular C60-Co films in the current perpendicular to plane (CPP) geometry. At low T, each sample shows 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 (T=2K), which changes depending on the sample composition and device structure. By considering this enhancement effect, we can estimate the spin-polarization at the C60-Co compound/Co interface. The estimated values are remarkably high, i.e., P=75% at zero temperature, compared to Co crystal(P=30%), and almost independent of the samples. The detailed results on the transport properties and X-ray magnetic circular dichroism spectroscopy were presented in the conference.