Papers by Keyword: Manganite

Abstract: It is known that magnetic, electric and optical properties of materials from mixed oxides mainly depend on the synthesis method used, therefore it is important to perform studies about the use of several synthesis routes with the purpose to understand and control the obtention of any given phase. In many of these routes it is required to control parameters such as temperature, pH, the variation of dopant concentration, etc. By this reason, in this work the effect of the method for three different synthesis routes (chemical coprecipitation, mechanosynthesis and combustion) was studied. These methods were used in the obtention of calcium manganite doped with lanthanum of theoretical stoichiometric Ca_0.3La_0.7MnO₃, using metallic minerals like precursors. The obtained powders were analyzed and characterized by X-ray diffraction (XRD), particle size analysis (PSA), scanning electron microscopy (SEM) and electron paramagnetic resonance (EPR). The crystallographic study (XRD) showed the obtention of calcium manganite doped with lanthanum with orthorrombic type structure, observed by SEM, agglomerates formed by particles with sizes smaller to one micrometer. By EPR it was found that powders obtained by chemical coprecipitation method showed magnetic behavior, in contrast with the behavior obtained by other two methods used, finding also powders with greater purity and in shorter synthesis time with regards to the ones obtained by mechanosynthesis and combustion.

Abstract: We present the results of investigations of the spin-polarized current and spin dynamics in the hybrid structures ferrimagnetic insulator/ferromagnetic metal subjected to microwave radiation. We studied the La_0.7Sr_0.3MnO₃/Y₃Fe₅O₁₂ bilayer films on the Gd₃Ga₅O₁₂ substrate. It was experimentally established that under the action of spin pumping the resistance of the La_0.7Sr_0.3MnO₃ film changes. The value of ΔR is maximum in the sample with a La_0.7Sr_0.3MnO₃ layer thickness of 10 nm and sharply drops as the manganite film thickness is increased. The resistance decreases in the paramagnetic region and grows in the ferromagnetic region at temperatures below the metal-insulator transition point. The variation in the resistance of the manganite film can be attributed to the correlation of the spin dynamics and transport properties of conduction electrons in the structure.

Abstract: Thermopower α and magnetothermopower α/α were studied in the single-crystal Sm_0.55Sr_0.45MnO₃ samples, containing clusters of three types: ferromagnetic clusters with the Curie temperature T_C = 134 K, A-type antiferromagnetic clusters with the Neel temperature T_NA T_C and CE-type antiferromagnetic clusters with the T_NCE = 240 K. The curves of temperature dependence of α (T) and {α/α}(T) have extrema in the T_NCE-region: large maximum on the first and sharp minimum on the second. Negative magnetothermopower in minimum achieves the giant value 50% in magnetic field 13,2 kOe. It is shown that thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which exists charge order, displacing oxygen ions

Abstract: Influence the deposition of La³⁺ ions by monovalent K⁺ ions on magnetorefractive effect on magnetoreflaction and magnetotransmission modes in the infrared range for La_1-xK_xMnO₃ epitaxial thin-films (х=0.05, 0.10, 0.15 и 0.18) has been studied. It has been shown that the magnetorefractive effect, transversal Kerr effect and magnetoresistance reach the maximum in optimally doped films at highest Curie temperature. The good agreement between calculated in framework of magnetorefractive effect theory and experimental data takes place only for optimally doped films, with potassium concentrations of 15 % and 18 %. At the other doping levels the films become charge and magnetic inhomogeneous. Magnetic and charge homogeneity influence strongly on magnetooptical effects in films. The resonance-like lines in magnetoreflection spectra of films are connected with the shifting of reflection minimum before the phonon bands under a magnetic field has been observed.

Abstract: Structural optimization, magnetic ground state and electronic structure calculations of tetragonal PbMnO₃ have been carried out using local density approximation (LDA) implementations of density functional theory (DFT). Structural optimizations were done on tetragonal P4mm (non-centrosymmetric) and P4/mmm (centrosymmetric) structures using experimental lattice parameters and our results indicate that P4mm is more stable than P4/mmm. In order to determine the stable magnetic ground state of PbMnO₃, total energies for different magnetic configurations such as nonmagnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) were computed for both P4mm and P4/mmm structures. The total energy results reveal that the FM non-centrosymmetric structure is found to be the most stable magnetic ground state. The electronic band structure, density of states (DOS) and the electron localization function (ELF) were calculated for the stable FM structure. ELF revealed the distorted non-centrosymmetric structure. The band structure and DOS for the majority spins of FM PbMnO₃ showed no band gap at the Fermi level. However, a gap opens up at the Fermi level in minority spin channel suggesting that it could be a half-metal and a potential spintronic candidate.

Abstract: Double-layered La_1.8Ca_1.2Mn₂O₇ sample with a perovskite structure was synthesized by solid state reaction and electrical transport properties were investigated using 4-wire direct current (DC) and 2-wire alternating current (AC) measurement methods. The result reveals that the I-V characteristic of the La_1.8Ca_1.2Mn₂O₇ ceramic exhibits a linear behaviour above Curie temperature (T_C) while it shows a strong nonlinearity below T_C. The nonlinear coefficient increases with decreasing temperatures and reaches a maximum of 60.5 at 14 K for the limit of the experiment. We believe that a magnetically correlated Schottky barrier forming at the grain boundary is the main factor to control the transport properties for the La_1.8Ca_1.2Mn₂O₇ ceramic.

Abstract: Nanoparticles of La_0.6Sr_0.4MnO₃ (LSMO) with an equivalent average particle size of ~ 20nm were synthesized by nitrate-complex auto-ignition method. The structural and magnetic properties were investigated systematically. The X-Ray diffraction study coupled with the Rietveld refinement of XRD data showed that sample crystallize in a rhombohedral structure with space group of R-3C. The stretching and bending modes in Fourier transform infrared (FTIR) spectroscopy is observed which indicates the formation of the perovskite structure of LSMO. The nature of DC magnetization versus field M(H) plot for sample resembles qualitatively with ferromagnetic (FM) systems. The AC-susceptibility data obtained at different frequencies confirmed the presence of a frequencydependent freezing temperature around room temperature. Based on the interparticle interaction strength and phenomenological models (Neel-Brown, Vogel-Fulcher and Critical slowing down) the magnetic dynamic behavior of nanoparticles was characterized. By fitting the experimental data with mentioned models the possibility existence of superparamagnetic/spin glass states were considered. The obtained values from fitting performance showed that there is a strong interaction between magnetic nanoparticles of LSMO.

Abstract: . Perovskite manganite Pr_0.7Ca_0.3MnO₃ (PCMO) thin film nanostructures were grown on different substrates by chemical solution deposition to investigate its electrical switching properties. Planar structures consisting of Ag/Pr_0.7Ca_0.3MnO₃/Ag grown on SiO₂, Si (100), LaAlO₃ (100) and MgO (100) were characterized by grazing incidence X-ray diffraction, atomic force microscopy and electrical measurements. In each case, single PCMO phase formation and smooth surface morphology was confirmed by XRD and AFM, respectively. Four terminal current voltage characteristics of Ag/PCMO/Ag planar geometry exhibited a sharp transition from a low resistance state (LRS) to a high resistance state (HRS) with a high resistance switching ratios of the order of 950 for PCMO films grown on quartz was estimated at room temperature. High resistance switching ratios were found to depend on the substrate, suggesting a role of lattice mismatch for resistance switching. We have observed that higher mismatch lead to better resistance switching in this compound. The observed conduction characteristics provide direct evidence of substrate strain induce resistance switching in the Pr_0.7Ca_0.3MnO₃.

Abstract: Swift heavy ion (SHI) irradiation of materials induces variety of functionalities and tenability in advance materials. Recent observations of electrical switching in perovskite oxides have triggered a lot of interest for its potential use as non volatile random access memory (NVRAM). We report on the resistance switching induced by swift heavy ion SHI irradiation in La_0.7Sr_0.3MnO₃ (LSMO) thin films grown on SiO2 substrates by chemical solution deposition technique. Well defined hysteresis loops with sharp on-off transition in the I-V curves were observed for the sample irradiated with 100 MeV Ag⁺⁷ ions at 1x10¹² ions/cm2, indicating that the sample possess low resistance state (LRS) and high resistance state (HRS). Symmetrical resistance ratio (Rhigh/Rlow) of ~ 330% at -1.7 V has been achieved whereas the pristine samples showed only linear I-V characteristics. The RS is bipolar and may be attributed to SHI induced defects in the device. Such defect induced resistive switching has recently been proposed theoretically and our results are direct evidence of the phenomenon.

Abstract: This paper presents a short review of research work on the development of synthesizing the colossal magnetoresistance materials through sol-gel method. Although there are a lot number of methods available, sol-gel method has been widely used and some excellent work has been reported. Two different manganite systems, which are LSMO and PSMO, that have been prepared through sol-gel method was choose for the discussion purpose. It was found that both systems were successfully prepared via the sol-gel method. Both systems showing better magnetoresistance properties compare to sample prepared through solid state reaction. X-ray diffraction technique was used to study the structural characteristic. Atomic force microscope and field emission scanning electron microscope were used in order to investigate surface morphology. Resistivity as a function of temperature was measured by a standard four-probe method.