Doping-induced magnetic phase transition in poly(3-alkylthiophenes).

Abstract

The dopant-agent--\ensuremath{\pi} system magnetic interactions in ${\mathrm{FeCl}}_{4}^{\mathrm{\ensuremath{-}}}$-doped poly(3-alkylthiophenes) (PAT's) have been studied. In particular, PAT's were subjected to magnetic susceptibility and magnetization measurements. The main goal of the experiments was to obtain temperature and magnetic-field dependencies of the above-mentioned magnetic quantities. The PAT samples were doped with ferric trichloride to different doping levels. The susceptibility and magnetization studies have shown that in the doped conjugated system the transition from a paramagnetic phase to an ordered phase occurs as the temperature is lowered. The magnetic interactions observed are associated with the dopant-agent--charge-carrying-species antiferromagnetic coupling. The coupling is stabilized by a retro or forward virtual charge transfer between the impurity molecule and the polymer chain.