Ferromagnetism And Fluorescence Properties Of X-doped(X=Mg,Sr,Fe,etc) YMnO₃

Yttrium Manganese Oxide (YMnO₃) is a promising material for its rich electric, magnetic and optic properties. YMnO₃ is ferroelectric and antiferromagnetic simultaneously, and its properties change with the variety of its chemical composition and crystal structure. Recently, many material, such as YMnO₃, become intresting subject again with the rising of the new material which is not only ferroelectric but also ferromagnetic. In this study, we prepared the targets of YMnO₃ family by sintering and the thin film of YMnO₃ family by pulsed laser deposition (PLD), and investigated the influence of the different doping to the structure, fluorescence and ferromagnetism properties of YMnO₃ sample. In our work, the main results are as follows:1. YMnO₃ thin films with different structure depodited on Si (100) substrate by PLD at room temperature and annealed at different temperature. The influence of the structure to the fluorescence properties was studied. The results show that polycrystalline YMnO₃ thin films in which hexagonal phase and orthorhombic phase coexist can be obtained through post-annealing, which establishes the groundwork for the studying of fluorescence emission properties of YMnO₃ thin films with different structures in atmospheric pressure. And with increasing of the temperature, the ratio of orthorhombic phase to hexagonal phase varies considerably. At the same time, the results also show that fluorescence peaks existing in the wavelength range of 430-620 nm maybe originate from the Mn³⁺ ion. And the intensity of fluorescence peaks is enhanced with increasing of the temperature. However, the positions of fluorescence peaks remain invariable.2. Mg, Sr-codoped YMnO₃ thin films were prepared by PLD at room temperature and post-annealed, and the influence of the doping to the structure and fluorescence properties was studied. The results show that the Mg, Sr-codoping can repress the growth of YMnO₃ thin films at (004)-orientation. The repressing enhances with the increasing of the ratio of doping, and achieves the most effect when the ratio of doping is 35% of 45%. At the same time, the intensity of fluorescence peaks is enhanced with increasing of the ratio of Mg and Sr.3. YMnO₃ thin films with La-doping on the substrate Si(100) were prepared by PLD and post-annealed, and the influence of the doping to the structure and fluorescence properties was studied. The results show that the La-doping can accelerate the fluorescence emission originated from the Mn³⁺ ion. And in the scope of study, the intensity of fluorescence peaks can be enhanced with the increasing of the La-doping ratio.4. The powder sample of Fe-doped YMnO₃ were prepared through sintering at 1400℃, and the influence of the doping to the structure and ferromagnetic properties of samples was studied. The results show that polycrystalline Fe-YMnO₃ powder in which hexagonal phase of YMnO₃ and cubic phase of YFeO₃ coexist can be obtained. And with increasing of the Fe proportion, the ratio of cubic phase of YFeO₃ to hexagonal phase of YMnO₃ enhances considerably. The results also show that the ferromagnetic of samples becomes when the proportion of Fe is 30%. And the coercive force of Fe-YMnO3 can be enhanced with the increasing of the Fe proportion. But when the ratio of Fe is 90%, the coercive force diminishes abruptly and the M-H curve takes on wasp waist. The cause may be the reciprocity and competition between the antiferromagnetism of YMnO₃ with hexagonal phase and the ferromagnetism of YFeO₃ with cubic phase.