Cu低掺杂对La_(0.7)Ca_(0.3)MnO_3电阻及磁电阻的影响

Effect of Low Cu Doping on the Resistance and Magnetoresistance Properties for La_(0.7)Ca_(0.3)MnO_3

用溶胶凝胶法制备了Cu低掺杂的La0.7Ca0.3Mn1-xCuxO3(x=0%, 1%,2%,3%,4%,5%)系列多晶材料.采用振动样品磁强计测量了系列样品的热磁曲线并获得了相应的居里温度,实验结果表明居里温度随着Cu掺杂量的增加而减少.在77～350 K温度范围内测量了样品的电阻和磁电阻,结果表明样品电阻率与温度的关系均具有明显的电阻峰结构.当x=5%时,开始出现双电阻峰结构;掺杂量x为1%,2%,3%,5%的样品在外场为0.4 T时存在较大的磁电阻极大值,分别为30.5%,25.4%,22.4%,18.8%,均大于未掺杂(x=0%)的13.5%.双交换(DE)模型简单地解释了Cu低掺杂对电阻及磁电阻行为的影响.

A series of polycrystal bulk samples of La0.7Ca0.3Mn1-xCuxO3（x=0%,1%,2%,3%,4%,5%） have been prepared by Sol-Gel method. The behaviors of the temperature dependence of the magnetization for all the samples were measured using a vibrating sample magnetomerer （VSM）. It is found find that the Curie temperature （Tc） of the samples La0.7Ca0.3Mn1-xCuxO3 decreases with increasing substitution content. The temperature dependences of resistance and magnetoresistance （MR） were measured from 77 K up to 350 K . The measurement results indicated that the obvious peaks exist in the resistivity-temperature and a double peak appears when the substitution content is 5 %. Also, it was found that the maxima of the magnetoresistance near the Curie temperature for samples La0.7 Ca0.3Mn1-xCuxO3 （x=1%, 2%, 3%, 5%） are quite large, being as high as 30.5%, 25.4%, 22.4%, 18.8% respectively under an applied field of 0.4 T, which are larger than one for the undoped sample with x = 0% （KMR=13.5% ）. The experimental results were explained simplely by the double exchange model with the ion doping.