Magnetoelectric and HR-STEM investigations on eutectic CoFe2O4-Ba1-xSrxTiO3 composites

Multiferroic Ba1-xSrxTiO3-CoFe2O4 (x = 0.03, 0.05) composites with rarely investigated 3-3 connectivity were prepared by eutectic crystallization in an optical floating zone furnace. High-resolution scanning transmission electron microscopy investigations of the CoFe2O4-BaTiO3 interface revealed an almost perfect connection between both components. These micrographs also showed that the impact of post-annealing in air was much larger than expected and resulted in formation of small BaTiO3 inclusions in the CoFe(2)O(4 )phase. The magnetoelectric coefficient alpha(ME )was studied in detail with respect to its dependence on the static magnetic field, the frequency of the driving AC-field and temperature. Furthermore, the influence of different growth rates (5, 10 and 20 mm h(-1)), chemical composition, sample thickness and the alignment of electrical polarization and magnetic field (collinear or vertical) on the magnetoelectric properties were studied. The largest value of alpha(ME) = 1.3 mV Oe(-1) cm(-1) was found for a sample grown at 5 mm h(-1). For even slower growth rates, a higher Sr content was required to avoid the formation of impurity phases leading to a decrease of alpha(ME).