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Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach. 相似文献
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高阻相对La2/3Ca1/3MnO3低场磁电阻效应的影响 总被引:1,自引:0,他引:1
实验研究了La2/3Ca1/3MnO3系统晶界上掺杂(YSZ)对其输运性能和磁电阻效应(MR)的影响。样品是由溶胶.凝胶法制成的。通过对样品的电输运特性的测量表明,在掺杂量(x)低于2%时,掺杂引起电阻的增大并降低了金属.绝缘体转变温度;当掺杂量高于2%时电阻逐渐减小,且转变温度增加。而低场磁电阻效应随掺杂量增加,在x=1%时达到最大。 相似文献
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通过实验研究了零场下La位上Y掺杂对(La1-xYx)2/3Ca1/3MnO3(x=0.10,0.15,0.20)系统输运性质的影响.实验结果表明,所有样品高温时呈半导体导电,低温时呈金属导电;随La位上Y掺杂含量的增加,峰值电阻温度向低温方向移动,并且转变温度附近的峰值电阻大大增加.基于Zhang S的自旋-极化理论,对实验观察进行了定量分析,结果显示随La位上Y掺杂含量的增加理论曲线和实验数据符合越来越好.这表明随单电子eg带宽的变窄,自旋-极化效应逐渐加强. 相似文献
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The structure and disorder-order transformation of NdxFe60.5-x Pt39.5(x = 0, 0.5, 1.0, 1.5) alloys were investigated in situ by high temperature X-ray diffraction. The results show that the lattice parameter a of disordered γ phase (FCC, Al structure type) and the lattice parameter ratio c/a of ordered γ1 phase (FCT, L10 structure type) increase linearly with increasing Nd concentration, whereas the c/a ratio decreases with increasing temperature. The transition temperature from ordered FCT to disordered FCC decreases with increasing Nd concentration, but for alloys quenched rapidly from γ phase region into ice-water it increases with increasing Nd. 相似文献
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The effect of Nd addition on the structure, phase transformation and magnetic properties of FePt based alloys was investigated. The results indicated that the transition temperature from ordered FCT to disordered FCC phase decreased with increasing Nd concentration, but for alloys quenched rapidly from the γ phase region into ice-water, it increased with increasing Nd. The Nd element not only effectively reduced the grain size of the ordered phase but also decreased the degree of the ordered phase and refined the grains of the FCC matrix phase. The remanence ratio and coereivity of the FePt based alloy as a function of the Nd content had maximum values, respectively. 相似文献