Preparation And Characterization Of Multiferroic Materials

Multiferroic materials are materials which exhibit both magnetic order and ferroelectricity in the same phase, and exhibit magnetoelectric (ME) effect between two phases. Magnetoelectric multiferroics are expected to have broad prospect of application for informated storage,spintronic device,magnetic sensor,capacitance-inductance integration device and microwave technology area. But the magnetic phase-transition temperature in single-phase multiferroic is very low, most of the multiferoic ME effect occurs at low temperature. This thesis is trying to explore the new multiferroic candidates based on the latest status of the research, and make it realize strong multiferroic property at room temperature. On the one hand, the single-phase multiferroics is synthesized by the technical innovation based on the lastest achievements of the international research, and its multiferroic properties are characterised by the new research methods; On the other hand, the composite multiferroics is synthesized to adopt the new magnetic phase, and its multiferroic properties are characterized. The three kinds of the single-phase multiferroic materials and a kind of composite multiferroic material adopting new magnetic phase were found through the study, and they have very good multiferroic properties at room temperature. The research contents and results of the multiferroic materials include:1.Preparation and characterization of nanocrystalline PbTiO3 ceramicFirst, nanocrystalline PbTiO3 powders have been successfully synthesized by the polymer precursor method using glycerin as a solvent and calcining at 450℃. The glycerin can reduce the calcination temperature. The sintering temperature can effectively control particle size and density. The magnetic and ferroelectric tests show that the magnetic polarization and electric polarization increased with a reduction in the grain size of PTO ceramics, and the magnetic polarization of nanocrystalline PbTiO3 ceramic improves with a reduction of the sintering temperature. Now, scientists have demonstrated that ferromagnetic might arise due to oxygen vacancies at the surface of nanoparticles of the nanocrystalline PbTiO3 ceramics.2.Preparation and characterization of single-phase multiferroic Pb2Fe205 ceramicFirst, Pb2Fe2O5 ceramic has been successfully synthesized by the polymer precursor method using glycerin as a solvent and sintering at 800℃. We demonstrate that ferroelectric properties occur in Pb2Fe2O5 through the ferroelectric test. Strong ferromagnetic property of Pb2Fe2O5 ceramic was also observed at room temperature through the magnetic test. In summary, Pb2Fe2O5 ceramic is a kind of multiferroic candidate, which could open a new field of research for room-temperature single-phase multiferroic material.3.Preparation and characterization of single-phase multiferroic PbFe12O19 ceramicPbFe12O19 ceramic has been successfully synthesized by the polymer precursor method sintering at 1000℃. The ferroelectric test indicates that it has a nature ferroelectric. The research of the crystal structure model of PbFe12O19 presume that the ferroelectric might arise due to Fe cation shifes away from the center along b axis, while O3 and O4 shifts off their original positions of octahedron along opposite directions of a-axis, which leads to the distortion of O5-Fe-O6 bond away from straight line. Strong ferromagnetic of PbFe12O19 ceramic was also observed through the magnetic test. In summary, PbFe12O19 ceramic is the best of single-phase multiferroic material at room temperature.4.Preparation and characterization of composite multiferroic PbFe12O19-PbTiO3 ceramicFirst, the magnetic-phase PbFe12O19 powder has been successfully synthesized by polymer precursor method using glycerin as a solvent. The composite multiferroics with magnetic-phase PbFe12O19 and ferroelectric-phase PbTiO3 has been successfully synthesized by the mechanical mixing method. The magnetic and ferroelectric tests show coexistence of ferroelectricity and ferromagnetism at room temperature, and the remanent polarization of ceramic increases with the increase of magnetic-phase contect, but the electric polarization of ceramic decreases. It opens up a new field of the reseash for particle composite ceramic with multiferroic properties.