Antiferromagnetic phases of one-dimensional quarter-filled organic conductors

The magnetic structure of antiferromagnetically ordered phases of quasi-one-dimensional organic conductors is studied theoretically at absolute zero based on the mean field approximation to the quarter-filled band with on-site and nearest-neighbor Coulomb interaction. The differences in magnetic properties between the antiferromagnetic phase of (TMTTF)(2)X and the spin density wave phase in (TMTSF)(2)X are seen to be due to a varying degrees of roles played by the on-site Coulomb interaction. The nearest-neighbor Coulomb interaction introduces charge disproportionation, which has the same spatial periodicity as the Wigner crystal, accompanied by a modified antiferromagnetic phase. This is in accordance with the results of experiments by Nakamura et al on (TMTTF)(2)Br and (TMTTF)(2)SCN. Moreover, the antiferromagnetic phase of (DI-DCNQI)(2)Ag is predicted to have a similar antiferromagnetic spin structure.