Resistive properties and phase diagram of the organic antiferromagnetic metal κ-(BETS)2FeCl4

The low-temperature electronic state of the layered organic charge-transfer salt κ-(BETS)2FeCl4 was probed by interlayer electrical resistance measurements under magnetic field. Both above and below TN=0.47 K, the temperature of antiferromagnetic ordering of 3d-electron spins of Fe3+ localized in the insulating anion layers, a nonsaturating linear R(T) dependence has been observed. A weak superconducting signal has been detected in the antiferromagnetic state, at temperatures ≤0.2 K. Despite the very high crystal quality, only a tiny fraction of the sample appears to be superconducting. Aside from a small kink feature in the resistivity, the impact of the antiferromagnetic ordering of localized Fe3+ spins on the conduction π-electron system is clearly manifested in the Fermi surface reconstruction, as evidenced by Shubnikov-de Haas oscillations. The "magnetic-field-temperature" phase diagrams for the field directions parallel to each of the three principal crystal axes have been determined. For magnetic field along the easy axis, a spin-flop transition has been found. Similarities and differences between the present material and the sister compound κ-(BETS)2FeBr4 are discussed.