Magnetic orderings of Fe3+ d spins in the 1:1 salts of BEDT-TTFVS(O) with FeX4– (X=Br, Cl) ions

Abstract We observed magnetic orderings of Fe 3+ d spins in the 1:1 salts of BEDT-TTFVS(O) with FeX 4 − (X=Br, Cl) ions by magnetization measurements up to 0.5 T in the temperature range down to 0.4 K using a homemade pulsed magnet system combined with a 3 He cryostat. Although temperature dependences of the magnetic susceptibilities above 20 K obeyed a Curie–Weiss law with positive Weiss temperatures, the salts were not subjected to ferromagnetic ordering but to antiferromagnetic orderings except for (BEDT-TTFVS)·FeBr 4 . The Neel temperatures, T N were determined to be 2.4, 1.0 and 0.8 K for (BEDT-TTFVO)·FeBr 4 , (BEDT-TTFVO)·FeCl 4 and (BEDT-TTFVS)·FeCl 4 , respectively. Below T N , a clear magnetization jump due to the spin-flop was also observed.