La_(2/3)(Ca_XBa_(1-X))_(1/3)MnO_3材料的绝缘体-金属转变与晶界效应

Insulator to Metal Transitions and Grain Boundary Effect in La_(2/3)(Ca_XBa_(1-X))_(1/3)MnO_3 Materials

用固相反应法制备了La2/3(CaxBa1-x)1/3MnO3(x=0.00,0.40,0.45,0.55,0.60,1.00)六种多晶CMR材料,并测量了在77K～350K范围内零磁场和0.4T外磁场下的电阻率。这些样品都出现了双电阻峰结构,采用Mott转变表达式ρ～exp(T0/T)1/4拟合了实验数据,结果表明高温峰的转变是绝缘体-金属(I-M)转变,而低温峰不是I-M转变峰,用自旋极化电子隧道效应和局域化模型解释了电阻和磁电阻行为。此外,在x=0.4～0.6掺杂范围内样品呈现出异常的电阻行为。

A series of polycrystal bulk samples of La2/3(CaxBa1-x)1/3MnO3(x=000,040,045,055,060,100)have been prepared by standard solid reaction method.The temperature dependences of resistivity and magnetoreisitance from 77K up to 420K have been measured respectively in the surrounding of H=0T and 0.4T.The temperature dependences of resistivity for the six samples appear double-peak.The resistivity property was fit by the Mott transition expression ρ～exp(T0/T)1/4 for La2/3(CaXBa1-X)1/3MnO3 samples.The results indicate that the resistivity peak in higher temperature (near 300K) is insulator to metal transitions,yet the resistivity peak in the lower temperature (near 210K)is not,which is explained well by the models of spin-polarized electron tunneling effect and localization.Also the anomalous resistance behaviors has been found in the doping region of x=0.4~0.6.