Periodic Kondo-Hubbard model for a quasi-one-dimensional organic ferromagnetm-polydiphenylcarbene: Cooperation between electron correlation and topological structure

Abstract

The ferromagnetic properties of a new organic polymer m-polydiphenylcarbene are studied by the periodic Kondo-Hubbard model. This polymer is designed so that coplanar benzene rings make a one-dimensional chain through a bridge made of a single carbon atom with a π electron and a nonbonding localized electron. The antiferromagnetic correlation between π electrons of the benzene rings and of the bridging carbon atoms is taken into account by the Hubbard model as is their itineracy, while the ferromagnetic correlation between the π electrons and the nonbonding electrons at the bridging carbon atoms is taken into account by the periodic Kondo model. Within mean-field theory, the ferromagnetic ground state is shown to be always stable as the result of cooperation between the two kinds of correlations and the topological structure of the carbon network. This theoretical result agrees with the observed spin density of a finite chain. The magnon is also studied within the random-phase approximation and is shown to have a large exchange energy, indicating that this material has a quite exotic magnetism.