Metallic Transport and Ferrimagnetic Interaction Achieved by Band Filling Control in Organic Conductors; β'-ET_3(MCl_4^<2->)_<2-x>(M'Cl_4^<1->)_x[M=Co, Zn, M'=Ga, Fe](Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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The systematic band-filling control has been performed in β′-ET_3(MCl_4^<2->)_<2-x>(M′Cl_4^<1->)_x (ET=bis-(ethylenedithio) tetrathiafulvalene, M=Co, Zn, M′=Ga, Fe, x=0-1.24). By means of band-filling control to the parent narrow-gap semiconductor, β′-ET_3(ZnCl_4^<2->)_2, the conductivity at room temperature (rt) is increased from 0.2Scm^<-1> to 50Scm^<-1> (M′=Ga, x=0.44) and the metallic behavior is observed down to 90K. The increase of resistivity below 90K caused by the randomness of the anion potential is suppressed by the external pressure and the metallic behavior is maintained down to 3K. The thermoelectric power measurements and their fitting based upon the band calculation demonstrate that the doping occurs at the two-dimensional donor layer and the one-dimensional array for β′-ET_3(CoCl_4^<2->)_<0.76>(FeCl_4^<1->)_<1.24>. Moreover, the introduction of the magnetic anions for β′-ET_3(CoCl_4^<2->)_<1.20>-(FeCl_4^<1->)_<0.80> affords the ferrimagnetic interaction between Co^<2+> (S=3/2) and Fe^<3+> (S=5/2) through the doped carriers.
2005-07-15