On the incorporation of iron into hexagonal barium titanate: II. Magnetic moment, electron paramagnetic resonance (EPR) and optical transmission.

Systematic measurements of the magnetic moment in dependence on temperature and magnetic field of hexagonal 6H-BaTiO3 + 0.04 BaO + x/2 Fe2O3 (0.005 ≤ x ≤ 0.05) ceramics were performed to study the influence of Fe ions on the magnetic properties. While the samples show Curie-Weiss paramagnetism for Fe concentrations ≤ 1.0 mol%, antiferromagnetic interactions become manifest for 2.0 and 5.0 mol% iron. With increasing Fe content the antiferromagnetic interaction, which is assumed to be caused by a superexchange mechanism Fe3+ Ti(1) - O2- O(2) - Fe3+ Ti(2), becomes stronger. At external magnetic fields smaller than 1 T a further, ferromagnetic interaction between Fe3+ ions is detected below 200 K. The interactions between Fe3+ ions in the samples with 2.0 and 5.0 mol% iron are also manifest in the EPR spectra by numerous lines with low intensity. Q-band EPR investigations of 5.0 mol% Fe doped single crystals confirm the existence of only one type of Fe3+ - VO associates in the samples.