Effect of cotunneling and spin polarization on the large tunneling magnetoresistance effect in granular C60-Co films

Seiji Sakai, Seiji Mitani, Isamu Sugai, Koki Takanashi, Yoshihiro Matsumoto, Shiro Entani, Hiroshi Naramoto, Pavel Avramov, Yoshihito Maeda

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)

Abstract

The tunneling magnetoresistance (TMR) effect of granular C60-Co films at low temperatures and also at small applied voltages is studied in the current-perpendicular-to-plane (CPP) geometry to elucidate the spin-dependent tunneling process, bringing about a remarkably high magnetoresistance (MR) as compared to the expectations from the conventional theory on sequential tunneling. The current-voltage characteristics showed ohmic and power-law dependences in the Coulomb blockade regime, which are interpreted as the occurrence of cooperative tunneling (so-called cotunneling) through a few to several Co nanoparticles. The zero-bias MR ratios are in the range of 50%-90% at a few degrees Kelvin and show strong and unconventional temperature dependence depending on the temperature range. Furthermore, the spin polarization of tunneling electrons evaluated based on the cotunneling model is in the range of 50%-80%, suggesting that the enhanced spin polarization of tunneling electrons at the interface between Co nanoparticles and a C60-based matrix (C60-Co compound) is crucial for large TMR effects.

Original languageEnglish
Article number174422
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume83
Issue number17
DOIs
Publication statusPublished - 2011 May 9

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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