Papers by Keyword: Manganite

Abstract: The sequence of Cu substituted Ca_0.9La_0.05Bi_0.05Mn_1-XCu_xO₃ ( x = 0, 0.025, 0.05, 0.075, and 0.1) manganite has been studied and it has effect in the structure. The samples was synthesized using the citric acid sol-gel method. The samples was sintered at 800 °C for 5 hours. The crystallography and morphological of all samples was investigated using X-Ray Diffractometer (XRD) and Scanning Electron Microscope (SEM). The Rietveld analysis of the powder x-ray diffraction shows that all the samples crystallize in orthorhombic structure with pnma space group symmetry without any impurity phase. The Cu substitution does not change the crystal structure, but it changes the grain size. SEM results showed a valid different morphological structure. The increasing Cu concentration, it made the grain size larger, dispite all the samples had the same treatment.

Abstract: Nanosized La_0.75K_0.05Ba_0.05Sr_0.15MnO₃ manganite have been synthesized using sol-gel method. Afterwards, the samples were sintered at eight different temperature ranging from 650 to 1000 °C. Phase purity, crystal structure and the morphology of the sample have been examined using X-Ray Diffractometer (XRD) and Scanning Electron Microscope. It has been found that different higher sintering temperature greatly affect the phase purity and crystallite size of the sample. Regardless of the sintering temperature, all the samples crystallized in rhombohedral structure with R-3c space group. The crystallite size of the samples is found to increase from 41.59 nm up to 73.42 nm as the sintering temperature increases. Further analysis from XRD result shows that sintering temperature also affect the average Mn-O bond length and Mn-O-Mn bond angle of the sample. The average Mn-O bond length is found to increase while the average Mn-O-Mn bond angle tends to decrease as sintering temperature increases. SEM measurement shows that various grain size ranging from ~100 nm up to ~ 350 nm exists in all the sample regardless the sintering temperature.

Abstract: The effect of Ru substitution on temperature coefficient of resistance (TCR) and electrical transport properties of Nd_0.67Sr_0.33Mn_1-xRu_xO₃ (with x = 0, 0.05 and 0.1) manganites prepared by solid state reaction route are studied. Ru substitution at Mn sites leads to reduction in T_P and increase the overall MR. The electrical transport mechanisms of these compounds are investigated by using different theoretical models, for temperatures below and above T_P. The maximum value of TCR of Nd_0.67Sr_0.33Mn_1-xRu_xO₃ (x= 0.05 and 0.1) are found to be higher compared to pristine compound. For memory device and bolometer IR detectors application point of view, all samples show the maximum magnetoresistance (MR) of 81 % at 5 T applied magnetic field, while the temperature coefficient of resistance (TCR) is found to ~17% K^-1.

Abstract: We report the electrical-transport and magnetic properties of the hole doped La_0.7Ca_0.3MnO₃ (LCMO-1) and La_0.88Ca_0.12MnO₃ (LCMO-2) single crystals, prepared using floating zone technique. The metal to insulator transition (T_MI) occurs at 211 K along c-axis and T_MI = 185 K along ab-plane for LCMO-1 single crystal. No electronic transition was observed over the whole temperature range under the magnetic field up to 8 T for LCMO-2 single crystal. It is observed that the T_MI is higher along c-axis as compared to that in the ab-plane, consequently signifying more favorable hoping of electrons is along c-axis in LCMO-1. The ac-susceptibility measurement shows that ferromagnetic to paramagnetic transition temperature (T_C) at 206 K for LCMO-1 and T_C = 118 K for LCMO-2 single crystals which is seemingly related to notable change of resistance at 120 K in LCMO-2 single crystal. The maximum MR of 98% for LCMO-1 and 59% for LCMO-2 single crystals up to 8 T applied magnetic field along c-axis and ab-plane, respectively are observed.

Abstract: Magnetic state of epitaxial heterostructures La_0.7Sr_0.3MnO₃/LaMnO₃/SrRuO₃ (LSMO/LMO/SRO) was studied by SQUID magnetometer, ferromagnetic resonance (FMR) and polarized neutron reflectometry (PNR) techniques. The fit of PNR and FMR data give us the magnetization of each layer, while the SQUID gives the total magnetization of our structures. The magnetic moment of the LMO layer has the magnetization 4πM_LMO=4.2kGs (2.4 m_B/Mn) at T=140K according to our PNR data fitting.

Abstract: The magnetic properties of the perovskite manganites LaMnO₃ (LMO) and La_2/3 Al_1/3 MnO₃ (LAMO) was presented. The calculations were made within density functional theory and generalized-gradient approximation (GGA) exchange correlations energy. It was found that LAMO exhibit magnetic properties and stabilizes in antiferromagnetic structure. However cell magnetization and magnetic moments reduce with inclusion of Al dopant.

Abstract: The electronic structure of the perovskite manganites LaMnO₃ and La_2/3 Al_1/3 MnO₃ was presented. The calculations were made within density functional theory (DFT) and PBE exchange correlations energy approximation. It was found that inclusion of Al dopants add additional states near the Fermi level and decreasing the resistivity values for all temperature range.

Abstract: The electronic structure of the perovskite manganites AlMnO₃ cubic crystal was presented. The calculations were made within density functional theory and PBE exchange correlations energy approximation. It was found that the crystal exhibit covalent bonding between Mn and O with superexchange mechanism. At groundstate, AlMnO₃ stabilizes in antiferromagnetic structure with semi metallic like nature at the ground state.

Abstract: The La_0.7M_0.3MnO₃ (M=Ca, Sr) were synthesized by combining sol-gel technique and solid state sintering method. The evolutions of phase structure and micro-morphologies of the La_0.7M_0.3MnO₃ with final sintering temperature (950-1250°C) were investigated. The results show that the La_0.7Ca_0.3MnO₃ compounds exhibit single perovskite phase with cubic structure and the La_0.7Sr_0.3MnO₃ compounds exhibit single perovskite phase with rhombohedra structure. The final sintering temperature has no obvious effect on the phase structure of La_0.7Ca_0.3MnO₃. However, the density and grain size of La_0.7M_0.3MnO₃ (M=Ca, Sr) increase with the increase of the final sintering temperature. Moreover, the micro-morphologies of La_0.7Ca_0.3MnO₃ are more sensitive to final sintering temperature compared with that of La_0.7Sr_0.3MnO₃. When sintering temperature is no less than 1150°C, the La_0.7Ca_0.3MnO₃ has hardly any pore. After sintering at no less than 1250°C, the La_0.7Sr_0.3MnO₃ becomes dense.

Abstract: We report the structural and thermo-power measurement of the ruthenium doped YMnO₃ compounds. The room temperature XRD study shows the single phase formation of the reported compounds with the incremental unit cell volume and lattice parameters attributed to the larger ionic radius of the Ru³⁺ (0.68 Å) and Ru⁴⁺ (0.62 Å) as compared with that of the Mn³⁺ (0.65 Å) Mn⁴⁺ (0.52 Å). The observed variation of lattice parameters provides us valuable information into the better consideration of the valence state of ruthenium, in these compounds. The thermo-power measurement reveals hole-like conduction mechanism for the thermo-electric transport.