title: Anomalous metallic-like transport of Co-Pd ferromagnetic nanoparticles cross-linked with π-conjugated molecules having a rotational degree of freedom.
abstract: We investigated the electron transport in Co-Pd ferromagnetic nanoparticles (Co 16%) cross-linked with oligo(phenyleneethynylene)diethanethiolate, which consists of three rotary phenylene moieties bridged by two acetylene groups, or icosane-1,20-dithiol, which consists of one alkane chain. Although the nanoparticles cross-linked with the alkane dithiols (the latter) have extremely high electrical resistance in electron transport, the resistance of the nanoparticles cross-linked with the conjugated molecules (the former) demonstrates a linear temperature dependence from room temperature to ca. 20 K; below that temperature, it has a weak temperature-dependent residual contribution with a resistance minimum around 7 K. Computational simulations suggest that the apparent metallic-like temperature dependence at high temperatures can be explained in terms of the rotational degree of freedom of the linker molecule. The rotational motion of the constituent phenylene groups, which hinders π-conjugation along the linker molecule, becomes less excited as the temperature is lowered. The successive development of a ballistic transport path through the π-conjugated linker molecule with decreasing temperature yields the metallic-like temperature dependence observed for the bridged nanoparticles. The low-temperature resistance behaviour with a minimum is a consequence of carrier scattering by the localized Co spins of Co-Pd nanoparticles randomly ordered in a ferromagnetic state that develops below the temperature of the resistance minimum.
authors.affiliation: Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan. ito@wpi-aimr.tohoku.ac.jp tenoki@chem.titech.ac.jp.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ito
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Takai
authors.forename: Akira
authors.initials: A
authors.lastname: Miyazaki
authors.forename: Vajiravelu
authors.initials: V
authors.lastname: Sivamurugan
authors.forename: Manabu
authors.initials: M
authors.lastname: Kiguchi
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Naotake
authors.initials: N
authors.lastname: Nakamura
authors.forename: Suresh
authors.initials: S
authors.lastname: Valiyaveettil
authors.forename: Tomofumi
authors.initials: T
authors.lastname: Tada
authors.forename: Satoshi
authors.initials: S
authors.lastname: Watanabe
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Enoki