Ag掺杂对La_(0.8)Ca_(0.2)MnO_3电输运性质及磁电阻的影响

Effect of Ag Doping on Electric Transport Property and Magnetoresistance of La_(0.8)Ca_(0.2)MnO_3

用固相反应法制备La1-x(Ca1-yAgy)xMnO3(y=0.0,0.2,0.4,0.6,0.8)系列样品,通过X射线衍射(XRD)谱,电阻率-温度(ρ-T)曲线,磁电阻-温度(MR-T)曲线,研究了在A位同时掺入一价、二价元素而保持Mn3+/Mn4+比值(摩尔比n(A)/n(B))不变的La1-x(Ca1-yAgy)xMnO3体系A位离子半径<rA>及A位离子的无序度σ2对电输运性质及磁电阻的影响。结果表明:所有样品的绝缘体-金属相变温度基本不变,用A位离子半径<rA>及A位离子的无序度对电输运性质影响的竞争给予解释;在0.8 T磁场下,y=0.0样品在133～26 K温区MR基本保持23%以上,y=0.6样品在209～131 K温跨区MR都在23%以上,在如此宽温区产生如此大的MR有利于MR的实际应用;MR的温度稳定性的机制是本征磁电阻与隧穿磁电阻竞争的结果。

Polycrystalline samples of La1-x（Ca1-yAgy）xMnO3（y=0.0,0.2,0.4,0.6,0.8） were prepared by the solid-state reaction method.The effects of the radius rA and disorder degree σ2 of A-site ions on electric transport property and magnetoresistance of the samples La1-x（Ca1-yAgy）x MnO3 with unchanged value of Mn3＋/Mn4＋ ratio through the introduction of both univalent and bivalent elements at A-site were studied through the measurements of X-ray diffraction（XRD） patterns,resistivity-temperature（ρ-T） curves and magnetoresistance-temperature（MR-T） curves.The results showed that the temperature of insulator-metal transition of all the samples basically kept unchanged,which could be explained by the competition between the effects of the radius of A-site ions rA and of the disorder degree of A-site ions on electric transport property.The MR of the sample with y=0.0 in the magnetic field of 0.8 T basically kept above 23% in the temperature range of 133~26 K,that of the sample with y=0.6 kept above 23% in the temperature range of 209~131 K,and so large MR appeared in such a wide temperature range,which was in favor of the practical application of MR.The mechanism of the temperature stability of MR was the result of the competition between the intrinsic magnetoresistance and the tunneling magnetoresistance.