STRONG CARRIER SCATTERING BY A CU2+ LOCAL MOMENT ARRAY IN ONE-DIMENSIONAL MOLECULAR CONDUCTORS CUXNI1-X(PHTHALOCYANINATO)I

We report microwave conductivity data (16.8 GHz) of the molecular conductors Cu(x)Ni1-x (phthalocyaninato)I obtained as a function of temperature (2-300 K) and magnetic field (0-10 T). Because of strong exchange coupling between the free carriers and the local moment array, the conductivity drops rapidly by orders of magnitude at intermediate temperatures; as the concentration of local moments x is decreased, this drop is shifted to lower temperatures and a very large positive magnetoconductivity is observed, in agreement with a magnetic scattering mechanism. At low temperatures (T < 10 K) the microwave conductivity is enhanced relative to the dc one; the magnetoconductivity is then negative and associated to a carrier relaxation through spin-wave generation since the local moments are indirectly exchange coupled by the carriers themselves.