Room-temperature multiferroicity in magnetic field-poled polyaniline and its enhancement via Cu2+-complexation

We report on the discovery of room-temperature multiferroicity in camphorsulfonic acid-doped polyaniline synthesized under an applied magnetic field of 0.5 T, increasingly enhanced via Cu 2+ -doping up to 8 wt%, probably as a nitrogen-coordinated square planar-like complex revealed by electron paramagnetic resonance spectra. Room-temperature switchable magnetization and polarization hysteresis cycles are presented, reaching saturated magnetization (polarization) of 0.019 emu/g (4.369 μC/cm 2 ) and coercivity (remanence) of 0.051 kOe (2.089 μC/cm 2 ) and revealing strong electric exchange bias. Both real and imaginary parts of permeability and permittivity exhibit resonance feature enhanced by Cu 2+ -doping, peaking at about the same position in the microwave range of 2–18 GHz and strongly suggesting magnetoelectricity. The proposed model picture, which accounts for both ferroelectricity and exchange bias, assumes ferromagnetic and ferroelectric orders within the same domain represented by crystalline polyaniline islands immersed within the amorphous polyaniline template. Modified Landau-Lifshitz-Gilbert equations account for the matching of permeability and permittivity resonance features.