Papers by Keyword: LaMnO₃

Abstract: We have studied the magneto-transport properties in LMO thin films on a-SiO₂ substrates produced by the metal organic decomposition (MOD) method. LMO thin films have been prepared by the MOD method in the 100 % O₂ gas atmosphere on different heat treatment conditions. Although LMO single crystal is an antiferromagnetic insulator, LMO thin films we have produced in the 100 % O₂ gas atmosphere by use of the MOD method shows the ferromagnetic metal properties for suitable heat treatment conditions. We consider that the excess of O^2- ions in LMO thin films produced in the 100 % O₂ gas atmosphere induces the strong hole self-doping into those and changes to ferromagnetic metal. The quantity of excess O^2- ions in LMO is sensitive to the heat treatment conditions of the LMO production, especially the temperature, time and atmosphere gas. We have obtained the coercive forces from the magnetic field dependence of magnetoresistance. Based on the temperature dependence of the coercive forces, we have estimated the Curie temperature of LMO thin films.

Abstract: We have studied the strong hole self-doping into LaMnO₃ (LMO) thin films produced by metal organic decomposition (MOD) method. With different heat treatment conditions, LMO thin films have been prepared by the MOD method in the 100 % O₂ gas atmosphere. We consider that the excess of O^2- ions in LMO thin films induces the strong hole self-doping into LMO ones. The quantity of excess O^2- ions in LMO is sensitive to the heat treatment conditions of the LMO production, especially the temperature, time and atmosphere gas. Although LMO single crystal is an antiferromagnetic insulator, LMO thin films we have produced in the 100 % O₂ gas atmosphere by use of the MOD method shows the properties of ferromagnetic metal.

Abstract: The structural and electrochemical properties of lanthanum manganate (LaMnO₃) powder prepared by the sol-gel method are researched in this article. The powder calcined at 600 °C showed amorphous, and the powder calcined at 700-800 °C showed the pure phase of the LaMnO₃. The grains with the size of about 80-120 nm were agglomerating together. Cyclic voltammetry and galvanostatic charge-discharge were used to characterize the electrochemical properties in alkaline environment. The electrochemical properties calcined at 700 °C showed a specific capacitance of 73 F/g at the current density of 0.5 A/g. The raw materials for preparing the LaMnO₃ powder are cheap, and the operation method is simple.

Abstract: In this paper, LaMnO₃/α-Al₂O₃ magnetic nanocomposites were synthesized through using a soft-chemistry route. The synthesis strategy in this work is based on a soft-chemistry process using a polyacrylamide gel route in which citric acid is employed as the chelating agent. The composites were characterized by thermogravimetric and differential scanning calorimetry analyses, X-ray diffraction, scanning electron microscope, energy dispersive x-ray spectroscopy and vibrating sample magnetometer. Scanning electron microscope observation reveals that the content of α-alumina decreases with the increase of number of sample surface particle in the composites. Magnetic hysteresis loop measurement shows that the LaMnO₃ sample exhibit paramagnetism at room temperature. Interestingly, the weak ferromagnetism at room temperature was observed for a composition of 0.7 α-Al₂O₃ / 0.3 LaMnO₃. The forming mechanisms and magnetic properties of α-Al₂O₃ / LaMnO₃ composites have been discussed based on the experimental results.

Abstract: LaMnO3-based perovskite oxides are typical functional materials applicable to various devices for its chemistry and physics properties. The conventional method solid-state reaction method has some drawbacks of high reaction temperature, large particle size and limited degree of chemical homogeneity. So, an easy, low cost and environmental method of synthesizing fine and homogenous powders of LaMnO3 is required. This paper discusses the synthesis of LaMnO3 via a mechanochemical activated process. The mixtures of La2O3 and Mn2O3 were used as starting powders. The specific surface of starting materials was measured by BET method. A planetary ball mill was used to grind the starting mixtures. During the grinding process, XRD analysis was employed to make clear the phase changes, and BET analysis was used to test the specific surface changes. After being grinded for different time, the mixtures were annealed at different temperatures. After this, the phase identification of mixtures was conducted by XRD. At the same time, a pre-mixing of starting materials with ethanol as solvent by normal ball-milling for 8 hrs was proceeded to obtain homogeneous mixture and improve the efficiency of grinding. All obtained LaMnO3 powders via the mechanochemical activated process were characterized by SEM imaging. Finally, an optimized powder processing was proposed.

Abstract: Samples of La(TixMn1-x)O3 (0.1 ≤ x ≤ 0.7) were sintered at different temperatures. The experimental results showed that the resistivity-temperature curves of the samples match NTC characteristic. The crystal structure was analyzed using X-ray diffraction and the microstructure was observed by scanning electron microscope.