Ferromagnetic polymers arising from magnetic and Coulombic interactions

We propose a model to investigate the magnetic behavior in the ferromagnetic polymer chain. Namely, the polymer consists of alternating single and double bonds, with Coulomb (Hubbard) intra-site interaction. Each repeat unit is further attached to a magnetic functional group, where the magnetic coupling between on-chain spin-polarized itinerant charges and localized magnetic moments of the size group is included. We found that dimerization opens a band gap in the polymers and is closely related to magnetism. Besides, the weakly linked magnetic functional groups can simultaneously increase the initially weak Coulomb interaction and the magnetic coupling to create significant magnetism in such ferromagnetic polymers. However, the strongly linked magnetic functional groups for creating ferromagnetic polymers can provide robust orbital coupling and produce significant orbital splits, but weak ferromagnetism of low-spin states appears. Moreover, choosing the light magnetic functional groups to link polymers can make effective dimerization as well as ferromagnetism. Furthermore, adding hole density to the polymers for increasing mobility does not have the same effect on rising Curie temperatures. Instead, a maximum Curie temperature appears on a specific hole density.