Magnetoelectric properties of bulk 0-3 Fe/BaTiO₃-composites

Magnetoelectric 0-3 Fe _<i>x</i> /(BaTiO₃)_1-<i>x</i> composites (<i>x</i> = 0.1-0.8) were synthesized by reduction of Fe₂O₃/BaTiO₃ pellets in forming gas. In a subsequent sintering step, dense composite ceramics were formed. Depending on the oxygen getter used in the sintering step (carbon or zirconium carbide) a partly iron-doped or undoped ferroelectric barium titanate matrix is obtained, which encloses micrometer-sized ferromagnetic Fe particles. The experimentally determined iron contents derived from Rietveld refinements and magnetic measurements are in good agreement with the nominal ones in the undoped composites. Field dependent magnetoelectric measurements revealed only small differences between the composites with doped and undoped BaTiO₃ component when the magnetic field and the polarization are oriented parallel to each other. For samples with iron-doped BaTiO₃, additional third extrema at low fields were found when the field was oriented perpendicular to the electric polarization whereas undoped samples exhibited only two extrema. The largest <i>α</i> _ME values were measured for the Fe _<i>x</i> /(BaTiO₃)_1-<i>x</i> composites with <i>x</i> = 0.4 (parallel) and <i>x</i> = 0.3 (perpendicular). Based on the integral of <i>α</i> _ME, the magnetostriction of iron and a phenomenological model describing the connection between magnetostriction and the magnetoelectric effect was derived. In temperature-dependent magnetoelectric investigations the low-temperature phase transitions of BaTiO₃ (tetragonal → orthorhombic → rhombohedral) were detected.