THEORETICAL-MODEL AND NUMERICAL-CALCULATIONS FOR A QUASI-ONE-DIMENSIONAL ORGANIC FERROMAGNET

A theoretical model is proposed to describe the quasi-one-dimensional organic ferromagnet polyBIPO. Different from Ovchinnikov's model, we consider the itineracy of pi electrons, the strong electron-phonon interaction, and electron-electron correlation in a one-dimensional system. Within the mean-field theory and Hartree approximation, allowing for full lattice relaxation, a set of self-consistent iterative equations is established to study the effects of pi electrons on the ferromagnetic order in the organic materials. The results of our calculations show that the ground state of the system is a stable ferromagnetic state. In the ferromagnetic ground state, the energy levels of the pi electrons will split off with respect to different spins. However, owing to the Peierls distortion of the lattice, all of the pi electrons will form an antiferromagnetic spin-density-wave chain.