To achieve ferromagnetism in organic polymers by doping: quantum chemistry studies

The ab initio many body perturbation theory method has been applied to a number of conjugated charged diradicals, which can be regarded as model molecules of doped systems. The intramolecular effective exchange integral (J) has been estimated by this method. In these diradicals, it is found that the J-value of two radical spins coupled through an odd number of conjugated atoms is ferromagnetic, while that coupled through an even number of atoms is antiferromagnetic. According to this simple topological rule some quasi one- and two-dimensional polymeric models have been proposed which can potentially be oxidized (or reduced) to ferromagnetic states by doping. This proposal has been further reasoned by ab initio unrestricted-Hartree-Fock crystal-orbital calculation for one of the models. The Curie temperatures have been estimated to be rather high for some two-dimensional models by the Ising approximation