Ca和Ba掺杂对La_(4/3)Sr_(5/3)Mn_2O_7的磁电阻效应的影响

Effect of the Ca and Ba doping on the magnetoresistance of La_(4/3)Sr_(5/3)Mn_2O_7

用溶胶-凝胶法制备了双层钙钛矿锰氧化物La4/3(Sr1-xAx)5/3Mn2O7(A是Ca或者Ba,x=0,0.1,0.2)系列多晶样品,并对其结构及电、磁输运性质进行了研究.研究结果表明:Ca和Ba的掺入虽然导致绝缘体-金属(I-M)转变温度(TI-M)降低,但可以明显提高低温区的磁电阻效应.对于x=0.2的Ca或Ba掺杂的样品,在60 K以下,磁电阻值接近100%,且为一恒定值.对于这一实验结果可以作如下解释:Ca或Ba掺杂引起了MnO6八面体的畸变,导致eg电子占据dx2-y2轨道和d3z2-r2轨道的状态偏离了x=0时的优化组合状态,铁磁性被削弱.

Double layered perovskite manganites La（4/3）Sr（5/3）Mn2O7 （A is Ca or Ba, x = 0,0.1, 0.2） polycrystalline samples were prepared by a sol-gel method, and its structure, electrical and magnetic transport properties were studied. With the doping of Ca or Ba, the insulator-metal （I-M） transition temperature （T（I-M）） is decreased, but the magnetoresistance effect is markedly improved in low temperature region. For the La（4/3）Sr（5/3）Mn2O7（A=Ca, Ba, x=0. 2） samples, the value of magnetoresistance is as high as 100% and remain invariableness below 60 K. The experiment results can be explained as the following： the doping of Ca or Ba causes the distortion of MnO6 octahedral, which leads to the status that eg electrons occupy the dx^2-y^2or dsx^2-r2 orbit deviating the optimized combination state and the ferromagnetism being weakened.