title: A giant negative magnetoresistance effect in an iron tetrabenzoporphyrin complex.
abstract: By measuring the electrical resistivity in TPP[FeIII(tbp)(CN)2]2(TPP = tetraphenylphosphonium and tbp = tetrabenzoporphyrin) under the application of a static magnetic field, a giant negative magnetoresistance (MR) effect with high anisotropy is observed. More specifically, the MR ratio at 13 K under a field of 9 T perpendicular to the c axis is -70%, whereas the MR ratio under a field parallel to the c axis is -40%. Furthermore, electron spin resonance (ESR) measurements indicate large anisotropy in the principal g-values of d spin (S = 1/2) in the [FeIII(tbp)(CN)2] unit; the g1value almost perpendicular to the tbp plane and the g2and g3values almost parallel to the tbp plane are 3.60, 1.24, and 0.39, respectively. It is revealed that the anisotropy in the MR effect arises from the anisotropy in the d spin, suggesting that the d spins in TPP[FeIII(tbp)(CN)2]2affect the π-conduction electron via the intramolecular π-d interaction. The anisotropy and magnitude in the giant negative MR effect for TPP[FeIII(tbp)(CN)2]2are smaller than the corresponding values for the isostructural phthalocyanine (Pc) analogue TPP[FeIII(Pc)(CN)2]2. This is consistent with the fact that the intermolecular antiferromagnetic d-d interaction in TPP[FeIII(tbp)(CN)2]2(suggested by the Weiss temperature: Θ = -8.0 K) is weaker than that in TPP[FeIII(Pc)(CN)2]2(Θ = -12.3 K). This indicates that the minor modification in coordination complexes can significantly affect the MR effect via tuning the intermolecular d-d interaction as well as the intermolecular π-π overlap.
authors.affiliation: Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan. masaki@sci.kumamoto-u.ac.jp.
authors.forename: Miki
authors.initials: M
authors.lastname: Nishi
authors.affiliation: Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Japan.
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Ikeda
authors.affiliation: Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Kanda
authors.affiliation: Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Japan.
authors.forename: Noriaki
authors.initials: N
authors.lastname: Hanasaki
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan.
authors.forename: Norihisa
authors.initials: N
authors.lastname: Hoshino
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Akutagawa
authors.affiliation: Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan. masaki@sci.kumamoto-u.ac.jp.
authors.forename: Masaki
authors.initials: M
authors.lastname: Matsuda