Study Of The Magnetic, Electric And Optical Properties And Their Coupling Effect In Doped-BiFeO₃

Multiferroics is a kind of multi-functional material, which contains two or more kinds of ferro properties, i.e.. ferroelectric, ferromagnetic and ferroelastic properties. In recent years, ferromagnetic and ferroelectric properties in magnetoelectric multiferroics have been well investigated and much achieves have been made in single phase and heterogeneous structures multiferroics. BiFeO₃ is one of the few materials which show both ferroelectric and ferromagnetic properties above room femperature. This multiferroics property above room temperature makes it possess potential applications. BiFeO₃. therefore, has become single phase material that is most widely investigated. In addition, it is reported that BiFeO₃ is a kind of narrow-gap ferroelectrics. and presents photovoltaic effect, which is new research field on photovoltaic effect in ferroelectrics. However, it is very difficult to synthesis pure phase BiFeO₃ ceramics. And the magnetism of pure phase BiFeOs is weak in room temperature. In this thesis, we tried to improve physical properties of BiFeO₃ single phase materials by preparation processes and doping element method. Then, based on these experimental results, the photovoltaic effect and magnetoelectric effect in doped BiFeO₃ single phase materials were well investigated. The main contents of the study are as follows:1. Single phase multiferroics Bi1-xLaxFeO₃ ?x=0.0.3? thin films deposited on ITO substrates have been synthesized through a Sol-Gel Dip-Coating ?SGDC? method+ rapidly annealing process. The structures of the thin films were investigated by X-ray diffraction ?XRD? and Raman spectrometer. Both BiFeO₃ and Bi_0.7La_0.3FeO₃ are pure rhombohedral perovskite structure. The basic physical properties, such as ferroelectric and magnetic properties of the thin films, were studied. The experimental results indicate that fine thin films with pure phase structure can be obtained by SGDC method with rapidly annealing process. The measurement results of magnetic properties confirm that La-doping at A-site of the sample can largely enhance the magnetization of the sample.2. Bi_0.85Cao isFeO₃ ceramic bucks were prepared by Sol-Gel method+rapidly annealing process. The results indicate that the magnetic property is enhanced after Ca-doped. which is similar to that in La-doped BiFeO₃. Especially, the modulation effect of electric field on magnetization, which had been widely observed in magnetoelectric composites, was also obtained in Bi_0.85Ca_0.15FeO₃ single phase multiferroics.3. Single phase multiferroics Bi_0.85Ca_0.15FeO₃ thin films were deposited on ITO substrates by using pulsed laser deposition ?PLD? method. The magnetic and ferroelectric properties, electric field modulation effect on magnetism, as well as ferroelectric photovoltaic effect, have been well investigated. These interesting results provide experimental basic for further investigation about multi-fields coupling among magnetic, electric and optical properties...