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Study on Preparation, Magnetic and Electrical Properties of La-Sr-Mn-O Composites and La-Ba-Mn-O Nanocrystals

Author: ZhaoXiaoLei
Tutor: ZhaoXu
School: Hebei Normal
Course: Condensed Matter Physics
Keywords: perovskite manganite oxides composites colossalmagnetoresistance nanostick and nanocrystals
Type: Master's thesis
Year: 2012
Downloads: 24
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As a typical strong correlated electron system, perovskite manganese oxideshows colossal magnetoresistance (CMR) effect, electron-orbital ordering, phaseseparation and multiferroic properties because of coupling among spin, electron, orbitand crystal lattice. The La1.3Sr1.7Mn2O7/La0.65Sr0.35MnO3composites andLa0.5Ba0.5MnO3nano-crystals have been synthesized by sol-gel and hydrothermalreaction, and the physical properties of these materials have been studied.(1) Two magnetic transition temperatures from low to high temperature inLa1.3Sr1.7Mn2O7/La0.65Sr0.35MnO3composites, and there is a platform between the twomagnetic transition temperature. With the increasing113phase, the magnetization onthe platform increases gradually. The magnetic coupling between the113and327phase occurs in the composites, and there is antiferromagnetic coupling at lowtemperature and ferromagnetic coupling at high temperature.The resistivity decreases gradually with the increasing113phase, and themetal-insulator transition temperature gradually shifts to higher temperature at thesame time and the peak gradually broadening in the composites. Themagnetoresistance has been improved from200K to room temperature compared tothe113and327phases. The magnetoresistance is3.45%(1T) and8.35%(3T) for thex=0.8sample at300K, which has the value of practical application for the composites.At the same time, magnetoresistance peak reached45%(1T) and65%(3T) for x=0.2sample at120K because of the small amount of113phase mixing.(2)The La0.5Ba0.5MnO3nanocrystal materials have been synthesized byhydrothermal. The shape and size of grain change with concentration of OH-. Whenthe concentration is less then22mol/L, the nanostick increases with the increasingconcentration of OH-for the samples. The nanostick begin to decrease until theconcentration of OH-is add to24mol/L and then keep on a constant. The size of grainfor14mol/L and18mol/L samples is in the range of0.3-3.5μm, which is greater then other samples.The sample of22mol/L have been sintered in different temperature, and thenanorods in this sample is decomposed at temperature of300℃. The grain boundaryof the sample begin to solution at900℃high temperature. The magnetization forLa0.5Ba0.5MnO3samples increase with the increasing size of grains and keep aconstant with the shape grains. The magnetization for the two bigger samples ishigher then other samples.

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