Investigation Of Ferromagnetic And Electric Properties For BaTiO₃-BaFe₁₂O₁₉ Multiferroic Composites

With the development of electronic information technology,electronic components meet the trend of miniaturization and multi-functional.Multiferroic magnetoelectric materials,which simultaneously exhibit two or more primaryferroics?including ferroelectricity,ferromagnetism and ferroelasticity?,have recently stimulated a sharply increasing number of research activities for their scientific interest and significant technological promise in the novel multifunctional devices.Multiferroic composites,which incorporate both BaTiO₃as piezoelectric phase and BaFe₁₂O₁₉ as magnetostrictive phase,typically yield good magnetic and electrical properties,which makes them ready for technological applications,including sensors and multiphase memories.The fact that the experimental values of multiferroic composites are lower than predicted can be attributed to a variety of factors including the formation of cracks,impurity phases at the interface between the two phases and the low resistivity of the ferrite phase.One way to accomplish this is to use some new preparation technique to inhibit reaction between two phases.Another effective way is to regulate multiferroic's structure.In this study,the microwave-assisted technology for preparing BaTiO₃-BaFe₁₂O₁₉ composites was studied.We focus on the preparation of BaTiO₃-BaFe₁₂O₁₉ composites with uniform structure and phases.BaTiO₃ and BaFe₁₂O₁₉nano-powders synthesized by microwave hydrothermal method are mixed by constructing a highly uniform ferromagnetic and ferroelectric system.A high-quality homogeneity ceramic composite material with less macroscopic defects,uniform phase and structure will be obtained by the microwave sintering technology in order to control two-phase grain size and inhibit the interface reaction and diffusion.The morphology evolution of nanoparticles by means of scanning electron microscopy?SEM?and transmission electron microscopy?TEM?were observed.The influence of connectivity schemes?0-3 type,3-0 type and 2-2type?and interface characteristics on the electric and ferromagnetic properties will be investigated by ferroelectric-dielectric and ferromagnetic measurements.Based on the results,it is possible to explain the electric and ferromagnetic properties deterioration problems for the mismatch between two grain size,phase heterogeneity and the decrease of electrical resistivity,the interface properties provide a theoretical basis for the design of new multiferroic materials.To explain the role of oxygen vacancies in the conduction mechanism of BaTi O₃-BaFe₁₂O₁₉ composites,the structural,morphological,conductive and magnetic properties of 0.7BaTiO₃-0.3BaFe₁₂O₁₉ ceramics were investigated as a function of oxygen vacancies by post-annealing in N₂ and O₂.BaTiO₃-BaFe₁₂O₁₉composites annealed in air and N₂ atmospheres show similar conductive characteristics,the increase in conductivity of BaTi O₃-BaFe₁₂O₁₉ composites annealed in air and N₂ is also related to oxygen vacancies.The values of conduction activation energy(E_cond=0.3 eV)suggest that the conduction process could be related to single-charged oxygen vacancies.All samples show ferromagnetic behavior at room temperature and the magnetization in proportion to the intensity of single-charged oxygen vacancies,ceramics annealed in N₂shows a 16%increase in magnetization.This reveals the important role of oxygen vacancie on the conduction mechanism and magnetic property of Ba TiO₃-BaFe₁₂O₁₉ multiferroic composites.The high dielectric loss and leakage current due to high concentration of the ferrite phase with low resistivity in the particulate composite ceramics can be eliminated by preparing in a range of composite architectures defined by the connectivity between the two phases.Space charge polarization plays a dominant role in aTiO₃-BaFe₁₂O₁₉ composites,the dielectric constant of BaTi O₃-BaFe₁₂O₁₉composites shows a broad peak in the range of 200³00 ^oC,which shifts toward high temperatures with increasing frequency.The permittivity and dielectric loss of the composites increased with the increase of BaFe₁₂O₁₉ contents.The homogeneous structure of 0-3 type?1-x?BaTiO₃-xBaFe₁₂O₁₉?x=0.02,0.04,0.60,0.80,0.10,0.12?composites effectively decreases the dielectric loss.3-0 type?1-x?BaTiO₃-xBaFe₁₂O₁₉?x=0.05,0.10,0.15,0.20?composites isolate the leaky ferrite phase within a ferroelectric matrix,which can hinder the long-range migration of carriers,decrease the dielectric loss and leakage current,and enhanced ferroelectric andferromagnetic properties.Compared with the dielectric loss of 0-3 type 0.90BaTiO₃-0.10BaFe₁₂O₁₉,the dielectric loss of 3-0type 0.90BaTiO₃-0.10BaFe₁₂O₁₉ composite decreased by⁵0%.The sample exhibits typical and enhanced P-E loops due to their good ferroelectric propertiy.The magnetodielectric coefficient is found to increase with increasing content of the magnetic phase.A maximum of magnetodielectric coefficient reaches up to5.3%for 3-0 type 0.90BaTiO₃-0.10BaFe₁₂O₁₉ composite at 1.8 T magnetic field.The magnetic and electric properties of the 2-2 type?1-x?BaTiO₃-x BaFe₁₂O₁₉?x=0.05,0.08,0.10,0.12,0.15,0.20?composites are more excellent than those of the 0-3 type and 3-0 type composites.Interface barrier in the interface between BaTi O₃ and BaFe₁₂O₁₉ can prevent the long-range migration of current carriers,which eliminates the leakage current in 2-2 type BaTiO₃-BaFe₁₂O₁₉ composites.The maximum magnetization of 2-2 type BaTiO₃-BaFe₁₂O₁₉ composites increased from 15.38 to 31.23 emu/g during BaFe₁₂O₁₉ content increases from 0.05 to 0.20.We found that the 2-2 type 0.9BaTiO₃-0.1BaFe₁₂O₁₉ composite exhibits lower dielectric loss at 10 kHz?⁰.3?,as compared with the 0-3 type?⁰.6?and 3-0 type?⁰.45?composites.The impedance of 2-2 type composite is almost two times of others.Observation of ferroelectric hysteresis loops confirms the ferroelectric nature for all the composites at room temperature.The magnetodielectric coefficient of samples increases with increasing BaFe₁₂O₁₉ content and magnetic fields,a large room temperature magnetodielectric coefficient over 6.71%is observed in 2-2 type 0.8BaTiO₃-0.2BaFe₁₂O₁₉ composite in 1.8 T magnetic field.By contrasting the magnetic and electric properties of BaTiO₃-BaFe₁₂O₁₉composites with different connectivity schemes,we confirm that the magnetodielectric mechanism in our composites is based on a“strain transfer effect”.The“strain transfer effect”can be described as:the applied magnetic field leads to a strain in the magnetostrictive component,and the stress at the interface related to this strain induces a dielectric polarization change in the piezoelectric component.