Cu掺杂LaMn_(1-x)Cu_xO_3体系的磁转变和导电行为研究

Magnetic transition and conducting behavior of the Cu-doped LaMn_(1-x)Cu_xO_3 system

系统研究了LaMn_(1-x)Cu_xO_3(x=0.05,0.10,0.20,0.30,0.40)体系的磁转变和导电行为.结果表明,在LaMnO3反铁磁母体中掺杂极少量的Cu(x=0.05)使该体系在157K左右出现强的铁磁转变,随着Cu掺杂浓度的增加,居里温度逐渐降低,而铁磁性则是先增强后减弱.与磁特性相对应,样品的电阻率随着Cu掺杂浓度的增加表现出先减小后增大的特征,并且在整个测量温区内始终呈现绝缘体型导电行为——从顺磁绝缘体到铁磁绝缘体;体系的导电行为在低掺杂(x≤0.10)时符合MottVRH(VariableRangeHopping)模型,较高掺杂时,又转而满足热激活模型.表明随着掺杂浓度的增加,由于Cu对Mn-O-Mn双交换作用和磁结构的影响,导致eg电子的输运由VRH模型的势垒作用占主导地位转变为热激活模型的能隙起主导作用.

The magnetic transition and conducting behaviors of LaMn1- x Cux 03 （ x = 0.05, 0.1, 0.2, 0.3, 0.4） system have been systematically studied. The results show that very small amount of Cu-doping （ x = 0.05） into the anti-ferromagnetic LaMnO3 matrix induces strong ferromagnetic transition below about 157K. The Curie temperature decreases gradually with the increase of Cu-doping content, while the magnetization increases firstly and then decreases. In accordance with the magnetic properties, the electrical resistivity decreases at low dopant （x ≤ 0.10） and then increases with the inerense of Cu-doping content. All samples exhibit insulating conducting behavior in the whole temperature range： frema paramagnetie insulator to a ferromagnetic insulator. The conducting behavior of lower doped samples （x ≤0.10） is well fitted by the Mott Variable Range Hopping （VRH） model, and then favors to the thermoaetivation model when 0.10 ≤ x ≤ 0.40. With the increase of Cu-doping content, the influence of Cu ions on the double exchange interaction among the Mn-O-Mn chains and the magnetic structure results in that the eg electron transport obeys the domination of potential barrier in the VRH model at lower doping and then favors the domination of energy gap in the thermal activation model at higher doping contents.