Preparation of multiferroic composites of BaTiO3-Ni0.5Zn0.5Fe2O4 ceramics

Magneto-electric coupling in ceramic composites formed by ferroelectric and ferromagnetic phases can be obtained via an adequate mechanical coupling between the individual piezoelectric and magnetostrictive phases (product property). In the present work, the possibility of forming diphase ferroelectric-ferromagnetic ceramics has been investigated. Composites of xBaTiO(3)(1-x)Ni0.5Zn0.5Fe2O4 with x = 0.5, 0.6 and 0.7 were prepared according two different procedures: (i) by direct mixing powders of perovskite BaTiO3 and Ni0.5Zn0.5Fe2O4 spinel prepared by solid state and (ii) by coprecipitating Fe-III-Ni-II-Zn-II nitric salts in a NaOH solution in which the BaTiO3 powders were previously dispersed. Optimum processing parameters for good homogeneity, densification and for a reduction of the chemical reactions at the interfaces ferroelectric-ferrite were found. A temperature and composition-dependent magnetic order is present in all the composites, with a dilution effect of the magnetisation due to the presence of the non-ferromagnetic phase. A diffuse ferroelectric-paraelectric transition due to the BaTiO3 phase was identified by the temperature-dependence of the permittivity and losses, showing that at room temperature the material preserves a ferroelectric order. The interfaces play important roles in the dielectric properties, causing space charge effects and Maxwell-Wagner relaxation, particularly at low frequencies and high temperatures. The combined ferroelectric and magnetic ordering will result in magneto-electric coupling in this material; further investigations are necessary. (c) 2006 Elsevier Ltd. All rights reserved.