Crossover from incoherent-metal to Fermi-liquid behavior in CuV2S4:: Transport and magnetic properties upon substituting Zn for Cu

We present the results of the measurements of electrical conductivity, thermopower, and magnetization of the Sulfospinel CuV2S4 and its Zn-substituted compounds between 2 and 600 K. We confirm the existence of two electronic transitions at around 90 and 54 K in the pure phase. The sharpness of the transition at 90 K is reduced by Zn substitution. Above 90 K the dependence of resistivity on temperature (T) in all the compounds is of the form rho(0)+A/T+BT-with anomalously large values of rho(0) and B. In the same temperature range the thermopower decreases linearly with increasing temperature and becomes negative above 500 K. These results regarding resistivity and thermopower are quite unusual for a normal metal. But they are reminiscent of the in-plane transport properties of high-T-c-cuprate superconductors and suggest highly incoherent dynamical behavior of current carriers in our compounds. These high temperature properties are also consistent with the presence of a pseudogaplike feature at the Fermi level-as has been seen earlier in the photoemission measurements in these compounds. Below 50 K the electronic properties are qualitatively different and can be understood in terms of a weakly correlated and exchange enhanced Fermi liquid. This inference is based partially on our analysis of the magnetization data at 2 K and high field (up to 7 T) in terms of the Stoner model of itinerant electrons. This analysis shows that the exchange splitting of the d bands is substantial and dominates the e-e repulsion-thus inhibiting a superconducting transition.