SQUID and ESR study of triplet paramagnetic centers in polyaniline

Abstract

Temperature and field dependences of magnetic moments of powders of the polyaniline base and polyaniline doped with acid HClO4 were measured by SQUID. The temperature dependences of the susceptibility were studied by ESR. A comparison of the susceptibilities determined by SQUID and ESR shows that a part of the susceptibility is not detected by ESR. This part is temperature-independent and, perhaps, is due to the Van Vleck paramagnetism. According to our and earlier published data for polyaniline and polypyrrole, the field dependences at helium temperatures are often characterized by the Brillouin function with S = 1, which cannot be explained in terms of the commonly accepted “metallic” model that predicts S = 1/2. It was established in this study that the field and temperature dependences can be explained in terms of the “triplet” model, and the absolute values of the mole moment are well simulated, i.e., not only the shapes of the dependences but also the values of the moment at different fields and temperatures.