@article{oai:nitech.repo.nii.ac.jp:00004713,
 author = {Peng, D. L. and Sumiyama, Kenji and Konno, T. J. and Hihara, Takehiko and Yamamuro, S.},
 issue = {3},
 journal = {PHYSICAL REVIEW B},
 month = {Jul},
 note = {We have fabricated CoO-coated monodispersive Co cluster assemblies with the mean cluster size of 13 nm at various oxygen gas-flow rate RO2 by a plasma-gas-condensation-type cluster beam deposition technique, and studied their electrical conductivity, σ, and magnetoresistance. For RO2<0.24 SCCM (sccm denotes cubic centimeter per minute), the resistivity revealed a minimum and showed In T dependence at lower temperatures, probably due to the weak localization of conduction electrons owing to presence of thin oxide shells covering Co cores. A small negative magnetoresistance was observed in this regime. For RO2>0.3 SCCM, tunnel-type temperature dependence of σ in the form of ln σ vs 1/T was observed between 7 and 80 K. This differs from the well-known temperature dependence of ln σ vs 1/T1/2 for disordered granular materials. The magnetoresistance ratio, (ρH=30 kOe-ρ0)/ρ0, is negative and its absolute value increases sharply with decreasing temperature below 25 K: from 3.5% at 25 K to 20.5% at 4.2 K. This marked increase, by a factor of 6, is much larger than those observed for conventional metal-insulator granular systems. These results are ascribed to a prominent cotunneling effect in the Coulomb blockade regime, arising from the uniform Co  core size and CoO shell thickness in the present monodispersed cluster assemblies., application/pdf},
 pages = {2093--2100},
 title = {Characteristic transport properties of CoO-coated monodispersive Co cluster assemblies},
 volume = {60},
 year = {1999}
}