Giant room-temperature magnetodielectric coupling in spark plasma sintered brownmillerite ceramics

摘要

The dielectric, magnetic, and magnetodielectric properties of CaFeAO (A = Al, Ga) ceramics were investigated together with their crystal structures. Rietveld refinement of the X-ray diffraction data indicated that the space group of the CaFeAlO ceramic was Ibm2, whereas that of the CaFeGaO ceramic was Pcmn. Dielectric relaxation above room temperature, originating from the Maxwell–Wagner effect and polaronic hole hopping between Fe and Fe ions, was observed in both ceramics. Weak ferrimagnetic behavior was identified from the magnetic-field-dependent magnetization in these ceramics, which was attributed to the non-cancelled spins of the antiferromagnetic-ordered Fe and Fe ions. An intrinsic, giant, room-temperature magnetodielectric coefficient of up to −23.3% was achieved in the CaFeAlO ceramic at 50 MHz, which was attributed to the suppression of charge fluctuations of Fe and Fe ions in the magnetic field.