| Co-Investigator(Kenkyū-buntansha) |
SAKURAI Masaki Institute for Materials Research, Tohoku University, Research Associate, 金属材料研究所, 助手 (80235225)
KONNO Toyohiko.j. Institute for Materials Research, Tohoku University, Associate Professor, 金属材料研究所, 助教授 (90260447)
HIHARA Takehiko Department of Materials Science and Engineering, Nagoya Institute of Technology, Research Associate, 工学部, 助手 (60324480)
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| Research Abstract |
In this research, we have elucidated the following points
1) We have installed two sorts of metal targets in the plasma-gas-condensation cluster deposition apparatus, produced alloy clusters with 5-10 nm in diameter, and deposited on a substrate. The transmission electron microscope observation and EDX analysis indicate characteristic aspects in comparison with the equilibrium phase diagrams : (a) the compositional fluctuation is not so marked and a B2-type ordered phase is formed in Co-Al (a compound formation type), (b) the compositional fluctuation is slightly detectable and a disordered fcc phase in Co-Pt (an ordered phase formation type), (c) the compositional fluctuation is enhanced and a fcc disordered phase in Co-Pd (a homogeneous solid solution type), and (d) the compositional distribution curve has double peaks, but the primary solid solutions are formed in Nb-Ag (an immiscible type).
2) Magnetization curves at 290 K as a function of the cluster size show ferromagnet-superparamagnet transition at around 8 nm in diameter.
3) Co core-shell cluster assemblies, Co CSCA, prepared by slight oxidation and deposition on a substrate, show a marked tunneling type conductivity and magnetoresistance with a Coulomb-blockade effect. It also shows a crossover from a thermal type to a quantum tunneling type magnetic relaxation.
4) The electrical resistivity measurement indicates that with increasing the degree of oxidation, Co, Ti and Cr CSCA changes from a metal (the temperature coefficient of resistivity, TCR, is positive) to a semiconductor (TCR is negative : an activation type), while Cu CSCA is always metallic. In the intemediate oxidation stage, TCR is positive at high temperature, while it become negative (-logT dependence) at low temperature, indicating a weak electron locarization effect. We are investigating their electronic states. These core-shell clusters will be useful for a tiny gas sensor and catalyses.
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