Magnetoelectric properties of Co1-xNixFe2O4/BaTiO3 heterostructures with 3-3 connectivity obtained by eutectic crystallization

Abstract

Multiferroic composites consisting of 62 mol% ferroelectric Ba0.97Sr0.03TiO3 and 38 mol% ferrimagnetic Co1–xNixFe2O4 with Ni substitution levels of x = 0, 0.25, 0.50, 0.75, and 1.00 are obtained from eutectic crystallization in a floating zone furnace. Scanning electron microscopy reveals the self-organized formation of a 3–3 network. Epitaxy of the two phases is confirmed by single-crystal X-ray diffraction. All samples, except the one containing pure NiFe2O4, are free of impurity phases. The influence of the substitution level x on the unit cell parameters of both materials is investigated by Rietveld refinement before and after a reoxidation process in flowing oxygen at 1173 K. The amount of oxide defects is determined by thermal analysis, showing a nearly constant value throughout the whole Co1–xNixFe2O4 series. The effect of Ni substitution on the magnetic properties (saturation magnetization and magnetic transition temperature) of the eutectics is investigated. The magnetoelectric (ME) properties of the samples are studied in dependence on the DC field (HDC), the frequency of the AC field (HAC), and temperature. The Ni content has a strong influence on the absolute value of the ME coefficient (αME), but only a slight effect on the general behavior of the ME properties.