| BiFeO3 is a kind of typical single phase multiferroic materials, simultaneously exhibiting ferroelectric and magnetic at room temperature. Due to its most promise application potential in spintronic devices, magnetic sensors and information storage, it has been one of the hot spot for materials research in the world. With the development of electronic device miniaturization and high integration, Nanomaterials have attracted extensive attention due to their unique properties. In recent years, a lot of studies on low-dimensional BiFeO3 nanomaterials were reported, such as BiFeO3 nanoparticles, BiFeO3 nanowires and BiFeO3 nanotubes. In this thesis work, we prepared undoped BiFeO3, Bi1-xNdxFeO3, Bi0.9Nd0.1Fe1-xCoxO3 and Bi1-xNaxFeO3 nanoparticles via a facile sol-gel method, and detailed studies of multiferroic properties of the samples were investigated.First, we studied the preparation conditions of high pure BiFeO3 nanoparticles via low cost and readily operate sol-gel method(with ethylene glycol as solvent, tartaric acid as complexant to prepare precursor solution). Based on this method, we prepared Bi1-xNdxFeO3(x=0, 0.05, 0.1, 0.15, 0.2) nanoparticles calcined at 500 and 600 ?, respectively, and detailed studies of magnetic and electrical properties were investigated. We found that the weak ferromagnetism of samples was due to the size effect which leads to the non-exact compensation in the nanoparticles' surface and the suppression of the spin helical ordering structure. The magnetization of samples calcined at different temperatures shows an opposite trend with the increase of Nd content, which is ascribed to the interplay of size effect and the ratio of Fe2+:Fe3+ in samples via XPS analysis. The dielectric properties were also measured and analyzed.Second, on the basis of Nd-doped BiFeO3 nanoparticles, we selected transition metals Co2+ ions to substitute Fe3+ ions and prepared Bi0.9Nd0.1Fe1-xCoxO3(x=0, 0.01, 0.03, 0.05) nanoparticles via sol-gel method, and the structure and microstructure were measured and analyzed. The samples show weak ferromagnetic behavior at room temperature. With the increase of Co doping concentration, the leakage of the sample is increased gradually. As the applied voltage is increased, the samples show threshold switching effects. Possible mechanisms for threshold switching effects are discussed on the basis of analysis of oxygen vacancies and impurity defects. From the UV-Vis absorption spectra, it is observed that the optical band gap decreases in the Co doped samples.Finally, we selected the highly aliovalent Na1+ as dopant to substitute Bi3+ ions and prepared Bi1-xNaxFeO3(x=0, 0.01, 0.03, 0.05) nanoparticles via sol-gel method carried out in our early work. We observed the weak ferromagnetic and exchange bias phenomenon in samples by measuring the field-dependent magnetization hysteresis loops at room temperature. To further ascertain the presence of exchange bias phenomenon, the training effect was investigated. Moreover, with the increase of Na1+ content, the band gap is decreased, while interestingly, the leakage current density is significantly reduced. To further explain the decrease of band gap and leakage current density, a phenomenological qualitative model based on the electronic energy band is proposed. |
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