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 ${Fe}_{Ti\left(1\right)}^{3+}-O_{O\left(2\right)}^{2-}-{Fe}_{Ti\left(2\right)}^{3+}$, 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⁺–V_O associates in the samples. (paper)