Magnetic and transport properties in double-doping La(2+4x)/3Sr(1−4x)/3Mn1–xCuxO3 (0⩽x⩽0.20) systems

A series of the double-doping samples La(2+4x)/3Sr(1−4x)/3Mn1–xCuxO3(0⩽x⩽0.2)(0⩽x⩽0.2)with the Mn3+/Mn4+ ratio fixed at 2:1 and the single-doping samples La2/3Sr1/3Mn1–xCuxO3(0⩽x⩽0.2)(0⩽x⩽0.2) have been investigated. For the double-doping samples, though the ratio Mn3+/Mn4+=2:1 has been generally recognized the optimum ratio, the Curie temperature TCTC and metallic–insulator transition temperature Tp1Tp1 are more rapidly decreased by Cu substitution than that corresponding to single-doping samples. And the resistivity ρρ value for the double doping is larger about two or three orders of magnitude than that corresponding to single doping. At the same time, two resistivity peaks and two magnetoresistance (MR) peaks appear. We suggest that for the double-doping samples the A-site cation size 〈rA〉 and the A-site mismatch factor σ2σ2 decreases with increasing doping level, which leads to the system microstructural distortion. This microstructural distortion makes the Mn3+–O–Mn4+ cut off more cluster-spin except for the clusters induced by Cu. These cluster interfaces contribute to ρρ, which exceeds far the contribution of eg electron decreasing with doping increasing in the single doping. At the same time, such interface scattering also gives rise to the appearance of second peak for the double-doping samples. The experimental results shows that double doping could be also a potential way in tuning colossal MR (CMR), which can give a guide for the adequate selection of CMR materials.