ANTIFERROMAGNETIC ORDERING AND SPIN STRUCTURE IN THE ORGANIC CONDUCTOR, KAPPA-(BEDT-TTF)(2)CU[N(CN)(2)]CL

The magnetism of an insulator, kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl, situ ated near the 10 K superconducting phase in kappa-type BEDT-TTF family , has been studied by H-1 NMR for the first time. A commensurate antif erromagnetic ordering with a moment of (0.4-1.0)mu(B)/dimer was found below 26-27 K. The features, quite different from the conventional spi n density wave, suggest that the magnetic order is driven by strong el ectron correlation rather than by nesting of the Fermi surface, and th at the present salt is a Mott insulator. Magnetization measurements sh ow spin canting parallel to the conducting layer below 23 K at low fie lds.