Oxygen content variation and cation doping dependence of (La)1.4(Sr1−yCay)1.6Mn2O7±δ (y=0,0.25,0.5) bilayered manganites (original) (raw)
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Materials Science-Poland, 2017
Polycrystalline bulk samples of double layered (DL) colossal magnetoresistive (CMR) manganites R1.2Sr1.8Mn2O7(R = La, Pr, Sm) were prepared by sol-gel method to study the effect of size of lanthanide ion on their magnetotransport properties. The electrical resistivity of the samples was investigated in the temperature range of 70 K to 300 K at different magnetic fields. The samples LSMO and PSMO show insulator-to-metal transition (IMT) behavior, while SSMO sample exhibits insulating behavior in the entire temperature range with a very large value of resistivity. The insulator-to-metal transition temperature (TIM) decreases from 123 K (LSMO) to 90 K (PSMO) and disappears in SSMO sample. To explain the electrical transport above TIM, the temperature dependent resistivity data (T > TIM) of all the samples were fitted to the equations of different conduction models. The results indicate that the conduction at T > TIMis due to Mott variable range hopping (VRH) mechanism in the LSMO...
Absence of long-range magnetic order in the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite
The journal of physical chemistry. B, 2006
This paper presents the results of a high-resolution neutron diffraction and magnetometry investigation on the optimally doped (x = 0.3) La(1.4)Sr(0.8)Ca(0.8)Mn(2)O(7) bilayered manganite. In particular, two samples with different oxygen contents have been studied to put in prominence the role of the Mn average valence states at fixed cation concentration. The results show, for the first time, the absence of long-range magnetic order in this optimally doped manganite when the A-site of the structure is doped with equal proportions of isovalent Ca and Sr. This holds for both samples, which present different lattice effects with T, thus suggesting the primary role of cation disorder as the source of the lack of long-range order. The presence, for both samples, of defined insulating- to metallic-like transitions suggests that the transport properties are not linked to the evolution of long-range order and that two-dimensional spin ordering in the layers of the perovskite blocks may be ...