Magnetoelectric behaviour of 0–3 Co/BaTiO3 composites

Abstract

Reduction of Co₃O₄/BaTiO₃ in forming gas followed by sintering in flowing nitrogen with carbon as an oxygen getter was applied for the synthesis of magnetoelectric 0–3 Co_x/(BaTiO₃)_1−x composites (x = 0.1–0.8). Phase pure BaTiO₃ and a mixture of hexagonal and cubic Co were obtained with a void-free embedding of micrometer-sized ferromagnetic Co particles in the ferroelectric BaTiO₃ matrix. No detectable incorporation of Co in the BaTiO₃ matrix occurred and the nominal Co contents agree well with the experimental ones derived from Rietveld refinements and magnetic measurements. A complex field dependence of the magnetoelectric coefficient (α_ME) was found with at least two local maxima/minima plus a pronounced hysteresis when the magnetic field and polarization are oriented perpendicular to each other. The sample Co_0.5/(BaTiO₃)_0.5 exhibits the largest α_ME values. The low-temperature phase transitions of BaTiO₃ (tetragonal → orthorhombic → rhombohedral) can be observed in the temperature dependence of α_ME. In contrast to other composites, the integral of α_ME and the magnetostriction of (hexagonal) cobalt show a distinctively different behavior, which might be due to the additional presence of the cubic Co modification.