Grain size and interfacial interdiffusion influence on the magnetic and dielectric properties of magnetoelectric La_0.7Ba_0.3MnO₃-BaTiO₃ composites

We report on specific features of the dielectric and magnetic properties as well as magnetoelectric coupling coefficients (α^ME) of the La_0.7Ba_0.3MnO₃ (L)-BaTiO₃ (B) 2-2 type ceramic composite. The powder of L and B was synthesized by two different methods (solid state reaction and Pechini). Orthorhombic and tetragonal phases were observed for the separated phases L and B of the composite, respectively, for both synthesis methods. The characteristics of grain size and interfacial interdiffusion in the L-B-L composite obtained for different synthesis method were studied, showing that diffusion was a typically physical migration, which can be mainly controlled by the grain size. Anomalies in the observed dielectric behavior are attributed to the internal residual stresses and chemically inhomogeneous regions. The existence of a broad magnetic transition observed in the pure L phase and laminated L-B-L composite was also attributed to its small grain size. A comparison of the maximum transversal (α₃₁^ME) and longitudinal (α₃₃^ME) ME coupling coefficients, at room temperature, is also shown.