Researchers have created a conducting polymer known as polyaniline, which displays remarkable diamagnetic properties, allowing it to repel external magnetic fields. This characteristic is often linked to superconductors. In contrast to most conducting polymers that usually exhibit paramagnetism — a weak attraction to magnetic fields — this development represents a significant step towards producing a conducting material that reflects diamagnetism, which is the opposite of paramagnetic behavior.
Conducting polymers possess various attributes aside from their ability to conduct electricity. Studies have investigated their potential in applications such as light-emitting devices, shielding against electromagnetic waves, and materials resistant to corrosion. A prominent feature among these is paramagnetism.
The research team has previously established techniques for creating different conducting polymers. In this investigation, they successfully synthesized polyaniline, a widely studied conductive polymer, in the presence of iron sulfate, resulting in perfect diamagnetism — a trait that prevents external magnetic fields from penetrating the material. This behavior is similar to superconductors and differs from the paramagnetic properties usually seen in conducting polymers.
Using Superconducting Quantum Interference Device measurements, the team confirmed that the synthesized polyaniline exhibits a gradual negative change in its magnetic susceptibility starting from around 100 K (−173°C) and reveals perfect antiferromagnetism beneath 24 K (−249°C). Typically, conducting polymers, which also function as organic semiconductors, show significant temperature dependence in their electrical conductivity. As temperatures drop, their conductivity diminishes, while electrical resistance rises. However, the polyaniline developed in this study displayed little change in electrical resistance with temperature, with a notable decrease in electrical conductivity only at extremely low temperatures.
The finding of perfect diamagnetism in polyaniline is an extraordinary phenomenon not seen in traditional organic or inorganic conductive materials. There is a possibility that an unusual mechanism for perfect diamagnetism is involved, which could pave the way for innovative progress in the realm of conductive polymers.
This research received funding from the Japan Society for the Promotion of Science under Grants-in-Aid for Scientific Research (No. 23K04848).
