Authors: O.J. Lee, S.A. Halim, K.P. Lim, Z.A. Talib, A. Huda, I. Priscilla
Abstract: The significant influences of substituting low concentration Dy at La- site for
La0.667Sr0.333MnO3 perovskites compounds in structural, electrical and magnetoresistance properties
have been studied. The polycrystalline samples (La1-xDyx)0.667Sr0.333MnO3 with x= 0.00, 0.02 and
0.10 were synthesized via conventional solid-state reaction in bulk. This work measured their
resistivity properties with (below 1 Tesla) and without the presence of magnetic field (0 Tesla) as a
function of temperature, microstructure and particle distribution and structural distortion using four
point probe resistivity technique, X- ray diffractometer (XRD) and Atomic Force Microscope
(AFM). The resistivity in applied magnetic field or so-called magnetoresistance ratio is defined as
MR% = (Ro – RH)/RH x 100 was measured at 90K, 100K, 150K, 200K, 250K, 270K and 300K.
The highest MR% values for x=0.00, 0.02 and 0.10 are 15.3%, 15.5% and 20.6% at 1 Tesla
respectively. The metal- insulator transition temperature, TMIT correspond to >300K, 298K and
230K of sample with x= 0.00, 0.02 and 0.10 respectively were observed from resistivitytemperature
(R-T) curve.
93
Authors: Shao Qun Jiang, Xin Xin Ma, Ming Ren Sun, Gang Wang, Guang Ze Tang
Abstract: Polycrystal samples of La1-xSrxMnO3 (x=0.2, 0.3) have been synthesized using a sol-gel
method. The effect of sintering process on the sample microstructure and Sr doping on the
magnetoresistance for La1-xSrxMnO3 have been investigated. The results show that the increase of
sintering temperature and time can promote the crystallization of samples and reduce the content of
impurity. The additive of Sr makes Mn ion in materials relatively compact, and this causes the
distorted deformation of the materials structure. The magnetoresistance (MR) changes with the Sr
doping. When x=0.2, the maximum MR% of sample is about 43% and keep about 40% between
10~150K. At room temperature, the MR% will decrease to about 6.5%. When x=0.3, the order
magnetoresistance (OMR) effect occures above the room temperature.
1826
Authors: Xiang Hu Li, Dan Li
Abstract: The compounds of Fe substitution of Al in nanotructured Sr2Fe1-x Al xMoO6 (0≤x≤0.2) double perovskite have been prepared by sol-gel method. The x-ray diffraction patterns of the samples show that the samples are in nanometer range. The Curie temperature and thesaturation magnetization of the samples decrease with the increasing of Al substitution. And the magnetoresistance of the samples increase with the increasing of x.
341
Authors: Shao Qun Jiang, Gang Wang, Qi Zhang, Jun Nan Hou, Ze Hua Wang
Abstract: The La0.8SrxCa0.2-xMnO3 (x=0, 0.05 and 0.15) compounds were synthesized by combining sol-gel method and high temperature sintering. The effects of Sr doping content on the microstructure, metal-insulator transition and magnetoresistance (MR) of the La0.8SrxCa0.2-xMnO3 were investigated. The results show that the La0.8SrxCa0.2-xMnO3 exhibit single perovskite phase and the change of Sr doping content can result in phase structure transition. The La0.8Sr0.15Ca0.05MnO3 is rhombohedra structure and the La0.8SrxCa0.2-xMnO3 shows distorted cubic structure when x is no more than 0.05. Increasing Sr doping content causes the degeneration of microstructure homogeneity and density and the decrease of average grain size of the La0.8SrxCa0.2-xMnO3, which can be attributed to the weakening of atomic diffusion during the sintering process. The metal-insulator transition temperature (TMI) of the compounds increases with the decrease of Sr doping content due to the improvement of microstructure. The La0.8Sr0.15Ca0.05MnO3 has the highest MR peak value, which is about 95%. The La0.8Ca0.2MnO3 has the highest room temperature MR, which is about 28%. Moreover, the magnetoresistance of the La0.8Ca0.2MnO3 is very stable between 125~300K.
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