The ferromagnetic behaviour of conducting polymers revisited

Abstract

The magnetic properties of doped pellets of poly(3-methylthiophene) showing roomtemperature ferromagnetic behaviour have been discussed in a previous article. Themagnetic behaviour was attributed to a weak ferromagnetic phase, due to thesuperexchange interaction of polarons via the dopant anions. The Dzialoshinsky–Moryainteraction among canted spins was proposed to explain the ferromagnetism. In thisarticle the main conclusions of that work concerning the magnetic behaviourare revised. The basic assumption now is that the magnetic moments are spin1/2 polarons that can interact antiferromagnetically and/or ferromagnetically. In the smallcrystalline regions of the polymer, which are identified with the polymer portionthat remains ferromagnetic at room temperature, the interaction gives rise toS = 0 and 1 bipolaronsand the S = 1 triplet state is lower in energy. In the disordered region, disorder will prevent the completeS = 1 and 0 coupling and bands of polarons ferromagnetically and antiferromagnetically coupledwill appear. Using this approach, all the magnetization data can be qualitatively explained,as well as the electron spin resonance data.