| In this dissertation, we have studied the theoretical model, mechanism and material design of the quasi-one dimensional organic ferromagnets for AB2 lozenge chain proposed by K.L. Yao, Y.F. Duan et al by using density matrix renormalization group. We have considered the itineracy of π-electrons, the e-e on-site repulsion, the e-e nearest-neighboring interaction and the e-p coupling in the molecular-based ferromagnetic model, then established a set of self-consistent iterative equations and detailedly investigated the magnetic ordering, the electronic structure, the spin correlation, and the effects of various interactions on the electronic structure and spin structure. Furthermore, we have also discussed on the relation of the doping effect and the stability of the ferromagnetic ground state of the system. Our research results show that there exists sign-alternating spin polarization cloud around the single lozenge block owing to the effect of this lozenge topology. Just owing to the coupling of this spin polarization cloud, the neighboring two sites are antiferromagnetically correlated and the whole system exhibits ferrimagnetic ordering. Therefore, a spin density wave along the main chain is formed. There exists a competition between the e-e on-site repulsion and the e-e nearest-neighboring interaction. The large e-e on-site repulsion and the small e-e nearest-neighboring interaction are in favor of the stability of the ferromagnetic ground state of the system. Doping can excite a charge density wave weakening the spin density wave against the stability of the ferromagnetic state. The e-e on-site repulsion can increase the amplitude of the charge density wave. In addition, for the doped system, the total spin of each unit cell is not 1/2。...
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