J. Phys. I France
Volume 2, Number 5, May 1992
Page(s) 741 - 751
DOI: 10.1051/jp1:1992177
J. Phys. I France 2 (1992) 741-751

Transport properties of the isostructural organic conductors Cu(L)I with itinerant charge carriers strongly coupled to Cu 2+ localized spins

G. Quirion1, M. Poirier1, C. Ayache2, K. K. Liou3 and B. M. Hoffman3

1  Centre de Recherche en Physique du Solide, Département de Physique, Université de Sherbrooke, Sherbrooke, Québec, J1K 2R1, Canada
2  Département de Recherche Fondamentale de la Matière Condensée, Laboratoire de Cryophysique, C.E.N.G., 38041 Grenoble, France
3  Department of Chemistry and Materials Research Centre, Northwestern University, Evanston, Illinois 60201, U.S.A.

(Received 16 October 1991, accepted in final form 13 January 1992)

We report the microwave and transport properties of the isostructural organic conductors Cu(L)I (L = phthalocyanine (pc), tetrabenzoporphyrinato (tbp), triazatetrabenzoporphyrinato (tatbp)). In these compounds the magnetic moments ( S = 1/2) of the Cu 2+ ions are found to be strongly coupled to the conduction electrons which results in dramatic effects on the transport properties. Whereas the conductivity at room temperature is found to be metallic, it decreases by several orders of magnitude below 100 K and shows a large positive magnetoconductivity. These effects are discussed in terms of scattering of the free carriers by the localized spins (Cu 2+, S=1/2). At low temperatures ( $T<10~{\rm K}$), we have also observed that the microwave conductivity is enhanced relatively to the dc one and it generally decreases with the magnetic field ; over the same temperature range the dielectric constant increases with the field. These effects at low temperature are rather believed to be related to a new relaxation mechanism between the chain of localized and the itinerant spins.

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