Bias voltage dependence of tunneling magnetoresistance in granular C₆₀-Co films with current-perpendicular-to-plane geometry

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• 作者：Seiji Sakai^a ; ^{sakai.seiji@jaea.go.jp} ; Seiji Mitani^b ; Yoshihiro Matsumoto^a ; Shiro Entani^a ; Pavel Avramov^a ; Manabu Ohtomo^a ; Hiroshi Naramoto^a ; Koki Takanashi^a ; ^c
• 关键词：Tunneling magnetoresitance effect ; Fullerene ; Cobalt ; Granular film ; Spin polarization ; Nanocarbon&ndash ; magnetic metal hybrid structure
• 刊名：Journal of Magnetism and Magnetic Materials
• 出版年：2012
• 期刊代码：31_03048853
• 类别：ph
• 出版时间：June, 2012
• 卷：324
• 期：12
• 页码：1970-1974
• 文件大小：407 K

摘要

Voltage-dependence of the tunneling magnetoresistance effect in the granular C₆₀-Co films has been investigated for the samples with the current-perpendicular-to-plane geometry. The transport measurements under this geometry demonstrate that the granular C₆₀-Co films show an unusual exponential bias voltage dependence of the magnetoresistance ratio down to zero voltage. Small characteristic energies of less than 10's meV are derived from the temperature dependences of the characteristic voltage in the exponential relationship. Considering the magnitudes of the voltage drop between Co nanoparticles and also the effect of cotunneling on the energy values, the characteristic energies for the voltage-induced degradation of the spin polarization are found to show a satisfactory agreement with that for the thermally-induced one. It can be reasonably expected that the onset of magnetic disorder to the localized d-electron spins at the interface region of the C₆₀-based matrix (C₆₀-Co compound) with Co nanoparticles leading to the unusual voltage and temperature dependence of the magnetoresistance ratio and the spin polarization at low temperatures.