Indication for an antiferromagnetically ordered state in the organic conductor κ-(BETS)2FeCl4

In this paper, we report on the magnetic properties of the organic conductor kappa-(BETS)(2)FeCl4, which were studied with a novel Faraday magnetometer in the temperature range from 0.6 to 40 K and under magnetic fields up to 7 T. Above 1 K, kappa-(BETS)(2)FeCl4 exhibits a Curie-Weiss behavior with an average Curie-Weiss temperature of about -1.5 K. Slightly anisotropic Curie-Weiss laws have been obtained for the field directions parallel and perpendicular to the conducting ac-layer. Below 1 K, spin-flop transitions have been observed in low magnetic fields (0.7 T) for the field direction perpendicular to the conducting layer, which indicates that the system is in an antiferromagnetically ordered state with the easy axis normal to the conducting layer. The Neel temperature is near 1 K. (C) 2000 Elsevier Science Ltd. All rights reserved.