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 CuxNi1-x (phthalocyaninato)I obtained as a function of temperature (2300 K) and magnetic field (010 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.