Electronic properties of BETS superconductors with magnetic anions (BETS=bis(ethylenedithio)tetraselenafulvalene)

The physical properties of BETS (=bis(ethylenedithio)tetraselenafulvalene) conductors with tetrahalide magnetic anions and related systems were investigated. We have recently succeeded to find the superconducting transition of the crystal of kappa-type TICl4- salt coated with epoxy resin (T-c(onset) = 2.5 K). The specific heat measurements on the antiferromagnetic organic superconductor, kappa-(BETS)(2)FeCl4 was performed down to 60 mK, which gave sharp peak at 0.45 K (T-N). The peak trails a tail at T > T-N, suggesting low-dimensionality of the spin system. Resistivity measurements under magnetic field of lambda-(BETS)(2)FeGa1-xCl4 (x approximate to 0.4) exhibiting superconductor-to-insulating (SC-I) transition, I-SC phase transition was observed around 4 T at T < 3 K. The "low-field superconducting region" between metallic and insulating phases around zero magnetic field is connected with the "high-field superconducting region". (C) 2002 Elsevier Science B.V. All rights reserved.