Papers by Keyword: Manganite

Abstract: The synthesis and characterization of the magnetic materials of La0.8Ba0.2Mn (1-x)TixO3 system (x = 0 0.7) by mechanical alloying process have been performed. This magnetic material is prepared by oxides, namely La2O3, BaCO3, MnCO3 and TiO2. The mixture was milled for 10 h and then sintered at 1000 ° C for 10 h. The refinement results of x-ray diffraction pattern showed that the doping concentration (x < 0.5) was a single phase, which has a structure monoclinic (I12/a1) with lattice parameters a = 5.5169(5) Å, b = 5.5437(5) Å and c = 7.8553(7) Å, = 90o and 89.75(1) o, V = 240.25(4) Å3 and 6.345 gr.cm-3. The microstructure analysis showed that the particle shapes was polygonal with the varied particle sizes distributed homogeneously on the surface of the samples. We concluded that the maximum number of titanium atoms substituting manganese atom is around x ~ 0.43 without changing the structure of this system.

Abstract: We report the magnetic transition and large magnetic entropy change in Sr doped lanthanum manganites. Polycrystalline La_1-xSr_xMnO₃ (0.20 x 0.35) samples were prepared using the conventional solid-state reaction method. The results of X-ray diffraction indicates perovskite phase without any impurity. The magnetic study has revealed that the Curie temperature is influenced by Sr-concentration. The doping of Sr at La site affects the Mn-O bond length and Mn-O-Mn bond angle due to the difference in their ionic radii, consequently, the Curie temperature changed. A large magnetic entropy change has been observed for La_0.8Sr_0.2MnO₃ sample, the value of the maximum entropy change (SMmax) increases from 1.42 to 2.74 J/kgK as magnetic field increases from 1 to 2.5 T. This investigation suggests that La_1-xSr_xMnO₃ can be used as a potential magnetic refrigeration material.

Abstract: In this paper, manganite (γ-MnOOH) nanowires have been synthesized, using KMnO₄ and CTAB as raw materials, by a hydrothermal method at 180°C for 12h. The samples were characterized by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscope (SEM),and thermogravimetric analysis (TG) for the information of crystal form, size, d-spacings, morphology and the weight-loss course. The results showed the manganite nanowires diameter range from 15 nm to 150 nm,length range from 5μm to 20 μm. Moreover, the properties of manganite (γ-MnOOH) nanowires as anode materials for Li-ion batteries had been studied. The first-discharge capacity is 1660 mAh g^-1 and corresponds to a consumption of about 5.5 moles of Li per mole of MnOOH, which made this material maybe one of the candidates for the negative materials.

Abstract: We report the results of the structural, transport and magnetotransport studies on mono-valent doped La_1-xNa_xMnO₃ (LNMO) (x = 0.05, 0.1 and 0.15) manganites. XRD measurement and Rietveld refinement on LNMO samples shows that, all the samples crystallize in distorted rhombohedral structure without any additional impurity peaks. The d.c. four probe resistivity measurements show that, the metal-insulator transition temperature (T_P) exhibited by the Na doped manganites increases and resistivity decreases with increasing x. This behavior has been explained on the basis of size disorder effect, tolerance factor variation and structural modifications due to large size mono-valent Na-doping. In the metallic region, the resistivity data have been fitted to the zener double exchange (ZDE) polynomial law for all the three samples. Magnetoresistance (MR) studies show a decrease in low temperature (5K) MR while increase in room temperature MR with increase in Na-content in the LNMO manganites.

Abstract: Thin films of La_0.8-xPr_0.2Sr_xMnO₃ (LPSMO) (x = 0.1, 0.2, 0.3) manganite, synthesized using pulsed laser deposition (PLD) technique, were irradiated by 200MeV Ag⁺¹⁵ ions with an ion fluence of 5 × 10¹¹ ions/cm². Structural and microstructural characterizations have been carried out using XRD and AFM show single crystalline nature of the films having island like grain growth. The structural and grain morphology modifications due to irradiation has been observed. Temperature dependent resistivity measurements have been carried out for all the films before and after irradiation, which reveal a reduction in the resistivity and enhancement in insulator - metal (I-M) transition temperature (T_P) with Sr content (x) resulting in improved transport (reduced resistivity and enhanced T_P) in the films which can be attributed to the irradiation induced improved crystallinity and grain morphology. Temperature coefficient of resistance (TCR) improves on irradiation which is useful for practical applications.

Abstract: Thin films of perovskite manganite La_0.9Hf_0.1MnO₃ (LHMO) have been grown on (100) SrTiO₃ single-crystal substrates with different growth pressures by pulsed laser deposition. The different transport behaviors of films have been fitted by various models. The results clearly demonstrate that oxygen pressure is an efficient way to change the transport behaviors of LHMO films. All the transport behaviors observed in LHMO films can be better fitted by Mott’s variable range hopping model than the other two models.

Abstract: The influence of cation inhomogeneity on magnetic and electron transport properties of (La_0.85Sr_0.15)_yMnO₃ (y=0.92-0.97) single crystals were studied. It was found that both the temperature of ferromagnetic ordering T_C and the temperature of orbital ordering T_OO are increased with the Mn content decreasing. For all six samples studied two peaks on magnetoresistance curves were observed: the first near T_C and the second close to T_OO. The magnetic field does not affect the position of the former maximum, while it moves the latter towards lower temperatures.

Abstract: Multiferroic YMnO₃ nanorods were synthesized by hydrothermal process at 200°C. Hexagonal structure of the synthesized sample was confirmed by powder X-ray diffraction analysis. High resolution scanning electron microscope analysis shows uniform nanorods with average diameter of about 350nm and length of 10µm. Transmission electron microscope and selected area electron diffraction studies reveal the single crystalline nature of nanorods and the lattice fringe width of nanorod is about 0.296nm for the (111) plane with the growth direction along (001) plane (c-axis). The zero-field-cooled and field-cooled magnetization studies show a complicated magnetic transition occurred in the temperature range from 20 to 300K as confirmed by magnetic hysteresis loops.

Abstract: Magnetic properties of polycrystalline Bi_0.5Ca_0.5MnO₃ are investigated by means of magnetization and electron spin resonance (ESR). The charge ordering (CO) and antiferromagnetic (AFM) transitions are determined from the temperature dependence of magnetization and ESR parameters. It is found that weak ferromagnetic (FM) spin correlations exist in the paramagnetic (PM) state. With temperature decrease, FM spin correlations are suppressed by gradually increased AFM spin correlations in the CO state and frozen in the long range AFM state at the AFM transition temperature TN. Our study suggests that the competition between FM and AFM spin correlations is accompanied by a change of spin-orbit coupling and spin-lattice interaction.

Abstract: Recently, it has been shown that the magnetorefractive effect in reflection and transmission modes in La_0.7Ca_0.3MnO₃ manganite thin films and single crystals can reach several percents for single crystals and up to 20-40% for thin films in the middle infrared spectral range near the Curie temperature. In the present paper, to explain these data we used the effective medium approach and supposed that La _0.7Ca _0.3MnO₃ manganites consist of low and high resistivity phases with volume fractions depending on an applied magnetic field. It is shown that the magnetorefractive effect spectra strongly depend on magnetoresistance and optical properties of manganites in the infrared range.