Anomalous charge transport phenomena in the molecular-based magnet V(TCNE)x.y(solvent)

We present charge transport studies on recently developed molecular-based magnets V(TCNE)x. y(solvent) (TCNE= tetracyanoethylene) which show local magnetic ordering at temperatures, T, as high as 400 K. V(TCNE), .y(solvent) prepared from the solvent CH2Cl2 has o(300 K) - 10-3 S/cm, and that prepared from the solvent CH3CN has o(300 K) - 10-5 S/cm. The o(T) of both materials follows the Mott 3D variable range hopping [log(T1/2o) o T-1/4] behavior. An anomalously strong T-dependent ac conductivity is likely caused by the short-range ferrimagnetic correlations. Cole-Cole analysis of the ac complex dielectric constant suggests there are two relaxation mechanisms, with an Arrhenius relation fitted to both. The microwave frequency response is consistent with audio frequency data and yields a localization length of - 5 A(o), comparable with the dimensions of a [TCNE]-. group.