Ca和Ba掺杂对La4/3Sr5/3Mn2O7的磁电阻效应的影响

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.

Effect of the Ca and Ba doping on the magnetoresistance of La4/3Sr5/3Mn2O7

Double layered perovskite manganites La4/3(Sr1-xAx)5/3Mn2O7(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(TI-M) is decreased,but the magnetoresistance effect is markedly improved in low temperature region.For the La4/3(Sr1-xAx)5/3Mn2O7(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 dx2-y2 or d3x2-r2 orbit deviating the optimized combination state and the ferromagnetism being weakened.