WEAK FERROMAGNETISM IN KAPPA-(ET)2CU[N(CN)2]CL, WHERE ET IS BIS(ETHYLENEDITHIO)TETRATHIAFULVALENE

Magnetization measurements at ambient pressure on kappa-(ET)2Cu[N(CN)2]Cl, an organic salt that is superconducting under pressure (T(c) = 12.8 K at 0.3 kbar), reveal an antiferromagnetic transition near 45 K and, for the first time in this class of materials, a transition near 22 K to a state displaying weak ferromagnetic hysteresis with a saturation moment of (8 x 10(-4)mu-B/formula. This low-temperature state is characterized by a sequence of first-order magnetization jumps.