Single-molecule tunnel magnetoresistance of p-type doped polypyrrole

Single-molecule electric current of pyrrole oligomers, as a model of p-type doped polypyrrole, was studied theoretically using the first-principles calculation method. Elementary excitations in doped polypyrrole, such as polaron and bipolaron, were modeled in this study as cation and singlet-dication, respectively. The oligomer was sandwiched between the ferromagnetic nickel electrodes, of which magnetic alignment was varied from parallel to antiparallel to confirm tunnel magnetoresistance (TMR) by a difference of electric currents under each magnetic configuration. Although the values of the electric current of the doping state increased compared to that of the neutral state, the TMR performance of the polaron state deteriorated compared to that of the neutral state, and the TMR performance of the bipolaron exceeded that of the neutral state. Therefore, it was found that the completed p-type doping state of the bipolaron improved the TMR effect performance.