IV-D Development of Magnetic Organic Superconductors

BETS-based salts incorporating Fe3+ ions are most interesting candidate systems for the observation of interplay of conductivity and magnetism. Indeed, in λand κ-(BETS)2FeCl4, conduction electrons in the BETS layers do interact with spins localised on the FeCl4 anions. Since the size of non-magnetic GaX4 anion (X = Cl, Br) approximatly equal to that of FeX4, (BETS)2GaX4 system can take the crystal structure almost identical to that of (BETS)2FeCl4. Furthermore we can prepare a series of BETS conductor with mixed-matal and mixed-halogen atoms. Systematic studies on λ(BETS)2FexGa1–xCl4–yBry have provided a number of interesting systems, including conductors with an antiferromagnetic metal state, a metamagnetic organic metal, and an antiferromagnetic organic superconductor. Unprecedented superconductor-to-insulator transitions and superconductor-to-metal transitions have been also observed. In this report the recent our studies on the BETS systems are reviewed. Figure 1. Temperature-magnetic field diagram of λ-(BETS)2FeCl4.