Magnetotransport Measurements on the λ-Phase of the Organic Conductors (BETS) 2 MCl 4 (M = Ga, Fe). Magnetic-Field-Restored Highly Conducting State in λ-(BETS) 2 FeCl 4

Magnetotransport properties of two isostructural salts, the superconducting λ-(BETS) 2 GaCl 4 phase and the first organic conductor containing magnetic Fe 3+ ions, λ-(BETS) 2 FeCl 4 , where BETS is bis(ethylenedithio)tetraselenafulvalene, have been studied up to 37 T. The previously reported sharp metal-insulator phase transition occurring at 8 K under ambient pressure for λ-(BETS) 2 FeCl 4 is suppressed when applying magnetic fields > 10 T. This unusual phenomenon may be connected to a field-induced ferromagnetic ordering of the Fe 3+ -ions moments. This could result in some kind of "decondensation" of the carriers, initially condensed below 8 K, into a field-restored highly conducting state (FRHCS). The temperature-magnetic-field (T-H) phase diagram is presented. The angle dependence of the critical field H c2 has been determined for the superconducting λ-(BETS) 2 GaCl 4 phase at 4.2 K.