Crystal orbital study on ferromagnetic state of poly(m-aniline)

The electronic structure of poly(m-aniline), the cationic and the dehydrogenated forms of which are considered to show ferromagnetism, has been theoretically examined using the one-dimensional tight-binding self-consistent-fieled crystal orbital method under the CNDO/2 approximation. It has been concluded that the ferromagnetic state would be energetically more favorable than the non-magnetic state in the cationic and the dehydrogenated forms, and the highest occupied ferromagnetic bands are extremely narrow because of the nature of non-bonding molecular orbitals. The spin is mainly located on nitrogen, but a considerable portion of the spin flows into the benzene ring through spin polarization mechanism. It is also clarified that a larger amount of spin is concentrated on nitrogen in the dehydrogenated form than in the cationic form. These results are in agreement with g-values observed by the ESR spectroscopy.