Magnetic field effects on nonlinear electrical transport in λ-(BEDT-TSF)₂FeCl₄, where BEDT-TSF is bis(ethylenedithio)tetraselenafulvalene

We have studied magnetic field effects on the nonlinear electrical transport associated with a negative resistance and switching phenomena in an antiferromagnetic insulating (AFI) ground state of the title π-d coupled conductor below the metal-to-insulator transition temperature T_MI = 8.3 K. The overall characteristics of current density (J) versus electric field (E) are well reproduced by an empirical formula with a current-density-dependent conductivity proportional to J_n; if n > 1, a negative resistance effect (dJ/dE < 0) appears above threshold J_T, while, if n < 1, a monotonic nonlinear resistance (dJ/dE > 0) appears. With increasing magnetic field, there appears a crossover from n > 1 to n < 1 around H* ≃ 7 T, followed by a conventional ohmic transport at fields higher than the critical magnetic field H_C = 10.6 T at 4.2 K for the reentrant metallic transition. A switching phenomenon, which always occurs at J < J_T in the well-ordered AFI states, triggers a discontinuous transition from low-conductivity to high-conductivity states, followed by the negative resistance at J > J_T which can be ascribed to a carrier's self-decondensation process.