Perovskite Manganese Oxide Nanomaterials :Preparation And Magnetic Studies

Perovskite structure manganese oxide has rich magnetoelectric properties, including ferromagnetic, ferroelectricity, colossal magnetoresistance effect, magnetocaloric effect, etc. All these properties make this kind of material has the very high potential value in industrial application, and become the hotest issue in the research of condensed matter physicists today.In this paper, we make the preparation of two groups of perovskite manganese oxide material namely La0.7-xSmxSr0.3MnO3(x=0.3) and La0.5Sr0.5MnO3, With the material La0.7-xSmxSr0.3MnO3(x=0.3), we studied the perovskite manganese oxide polaron transport mechanism and with the material La0.5Sr0.5MnO3, we studied the phase transition and magnetocaloric effect in nanocrystalline La0.5Sr0.5MnO3. The details are as follows:1.With the Sm element doped into the perovskite manganese oxide materials La0.7-xSmxSr0.3MnO3(x=0.3), the structure and nature have some changes, and based on the measurement of magnetic field, temperature resistance and electron spin resonance spectroscopy, we analyze the phenomenon of phase separation in the material of La0.7-xSmxSr0.3MnO3(x=0.3). The transport behavior in the paramagnetic region can be used to explain the polaron model. By constract, the activation energy deduce from double integral of resonance spectrum and from ρ(T) curves, this two activation energy are very close. This phenomenon supports the contention that the small polaron hopping model is appropriate to the transport behavior in PM region.2.We fabricated the material of La0.5Sr0.5MnO3 nanoparticles by sol-gel method and the temperature dependence inverse susceptibility and the EPR analysis exhibits a possible Griffiths singularity. This kind of phenomenon have never appear in the corresponding block material. We use nuclear shell model to analyses the Griffiths singularity and argued the phenomenon was caused by the surface of the spin disorder by local ferromagnetic fluctuations.3.Based on the research of the second part of La0.5Sr0.5MnO3 nanomaterials, we have carried on the detailed analysis about the magnetism and magnetic entropy change of the relevant material. From analysis on magnetic entropy change, the size reduction of samples was found to decrease the magnitude of MCE. Based on the obtained critical exponents, the PM-FM phase can be consider to be second-order. Besides, We have verified the agreement between two different methods for determining the spontaneous magnetization, including that the estimation of spontaneous magnetization from magnetic entropy change is valid for the material of second-order phase transition.