ELECTRIC AND MAGNETIC-PROPERTIES AND PHASE-DIAGRAM OF A SERIES OF ORGANIC SUPERCONDUCTORS LAMBDA-BETS2GAXZY4-Z [BETS=BIS(ETHYLENEDITHIOTETRASELENAFULVALENE, X, Y=F, CL, BR 0-LESS-THAN-Z-LESS-THAN-2)]

The physical properties of a series of organic superconductors with fo urfold quasistacking structures, lambda-BETS2GaXzY4-z [BETS=bis(ethyle nedithiotetraselenafulvalene; X,Y=F, Cl, Br; 0<z<2)] are changed conti nuously by tuning the value of z. The compound lambda-BETS2GaBrzCl4-z, has a superconducting ground state for 0<z<z(c) (approximate to 0.8) and a semiconducting state for z(c)<2<2.0. The maximum T-c is about 10 K, showing the existence of a 10-K class of non-ET organic supercondu ctors [ET=bis(ethylenedithio)tetrathiafulvalene]. The temperature depe ndence of the resistivity closely resembles that for kappa-type ET sup erconductors but the susceptibility behavior is different. The suscept ibility of lambda-BETS2GaBr1.5Cl2.5 is isotropic and decreases fairly sharply below 30 K. No indication of a spin-flop transition was observ ed at 10 K, suggesting that the insulating phase that neighbors the su perconducting phase is not antiferromagnetic at least dawn to 10 K.