Spin configurations of π electrons in quasi-one-dimensional organic ferromagnets

Based on a theoretical model proposed for quasi-one-dimensional organic polymer ferromagnets, the spin configuration of π electrons in a π-conjugated carbon chain with a single and two side radicals, which contains unpaired electrons, is investigated. The strong electron-phonon interaction and electron-electron interaction in the one-dimensional system are taken into account self-consistently. It is found that around the unpaired electrons there appears a π-electron spin-polarization cloud with alternation of the sign and the amplitude of the spin density extending over a certain distance, which reduces rapidly with the increasing of electron-phonon coupling. In order to obtain ferromagnetic order in this kind of material, the number of carbon atoms, which is intermittent between two neighbor side radicals, should be odd. It is shown that the π-orbital alternation will result in a Peierls transition which stabilizes the magnetic order.