Perfect Diamagnetism of Polyaniline

Herein, we report the synthesis of Fe-doped polyaniline (D-PANI). The onset of the diamagnetism is observed to be at <i>T</i> < 24 K under a weak external magnetic field. D-PANI was air-stable and showed the Peierls transition, as its resistivity increased rapidly at low temperatures, thus behaving as an electromagnetic insulator. The synthesized material showed high sensitivity to magnetic fields, with its diamagnetic character changing under a relatively low magnetic field (> 4.3 Oe) at 4 K. However, its resistivity remained almost constant at high temperatures, and the 1/<i>T</i> plots of conductivity indicated the nearest neighbor electron hopping conduction. Polarons (radical cations) in D-PANI behaved as localized charge carriers, showing perfect diamagnetism at low temperatures. X-ray photoelectron spectroscopy and X-ray fluorescence revealed that after purification, D-PANI contained C, N, O, S, and Fe but showed no electron spin resonance signal owing to its diamagnetism. Although superconductors show perfect diamagnetism, the synthesized PANI did not exhibit zero resistance; the perfect diamagnetism herein differed from the Meissner-Ochsenfeld effect. The polaron-derived perfect diamagnetism in a conductive polymer is a new magnetic phenomenon.