Results 1 - 10 of 86
Results 1 - 10 of 86. Search took: 0.017 seconds
|Sort by: date | relevance|
[en] Polycrystalline compounds La0.8Na0.2−x□xMnO3 were prepared by the solid-state reaction with 0.00≤x≤0.15. Structural, magnetic and electrical measurements were investigated. The XRD data have been analyzed by Rietveld refinement technique which reveals that all samples are crystallized in a rhombohedral structure with R3¯c space group. Magnetic measurement versus temperature shows that all samples exhibit a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase when increasing temperature. The Curie temperature (TC) decrease from 340 K for x=0.00 samples to 260 K for x=0.15 one. Hysteresis cycles confirm the ferromagnetic character at low temperature with a decrease of the remanent magnetization and the coercive field when the vacancy rate increases. Moreover, the temperature dependence of electrical resistivity shows a metal–insulator transition at Tρ for all samples. In addition, Tρ decreases with vacancy content in accordance with TC. Thus, the conduction mechanism was explained by the adiabatic small polaron hopping (ASPH) in the insulating region and by the competition between the small-polaron and spin-wave scattering and the electron–magnon scattering mechanisms. Finally, the minimum of resistivity at very low temperature range is explained by the Kondo-like scattering model
[en] Crystallochemical analysis of the binary compounds □2Cr12P7 and □6Rh20Si13 prompted us to introduce rare earth elements and zirconium into the trigonal prismatic metalloids in order to obtain ternary compounds. Our current study of the Zr, Ln-Ru-P systems shows the existence of many new ternary phosphides of formulae (Zr, La)2Ru12P7, (Zr, La)5Ru19P12, (Zr, Ln)6Ru20P13, (Ln = La, Ce, Pr, Nd, Sm and Y) and La20Ru66P43. All of them crystallize in the hexagonal lattice with structures of different arrangements derived from the same basic rhombohedral motif. The differences amongst these arrangements result from the introduction of different proportions of various metallic elements. (author)
[en] Based on the modified Arrott plots and the critical isotherm analysis, the critical exponents of both La0.5Ca0.5MnO3 and La0.5Ca0.4Ag0.1MnO3 systems have been comprehensively studied and investigated near the paramagnetic-ferromagnetic (PM-FM) phase transition. Critical exponents, β, γ, and δ, which are corresponding to the thermal variation of the spontaneous magnetization, initial susceptibility, and the isothermal magnetization, respectively, obeyed the Widom scaling law δ = 1 + γ/β. It indicates thus the validity the obtained results. We performed then another analysis of the critical behavior via the magnetocaloric effect presenting an accord with the analysis of magnetization measurements. Relative cooling power (RCP) follows the evolution of the magnetic field as RCP ∼ H1+1/δ. The acquired critical exponents were in conformity with those gotten from the modified Arrott plots and Widom scaling law.
[en] The effect of Cr doping on the structural, magnetic and magnetocaloric properties of perovskite manganites La0.75Sr0.25Mn1-x Crx O3 (x = 0.15, 0.20, and 0.25) has been investigated. Crystalline structure and magnetic properties are investigated by using X-ray powder diffraction and magnetization measurements, respectively. All samples show a single phase and are found to crystallize in the distorted rhombohedral system with R anti 3c space group. A monotonous change of Curie temperature (TC), from 314 to 253 K, is observed when content doping increases. Substantial magnetic entropy change reaching 4.20 J/kg K is revealed. Relative cooling power was estimated as well. It was found to reach 289, 323, and 386 J/kg for x = 0.15, 0.20, and 0.25, respectively. Field dependence of the magnetic entropy change showing the power law dependence ΔSM ∝ (μ0H)n is also analyzed and discussed. (orig.)
[en] Author.The effects of oxygen deficiency on structural magnetic and electrical properties of La0.7Sr0.3MnO3-δ□δ where □is a vacancy and 0 ≤ δ ≤ 0.15, has been investigated. We present a new method of creating vacancies in the oxygen sites achieved at atmospheric pressure. X-ray diffraction patterns reveal that these materials have a rhombohedral structure ∫ or δ ≤ 0.075 and orthorhombic when δ ≥ 0.1. The magnetization and resistivity measurements as a function of temperature show a ferromagnetic metallic behavior for δ ≤ 0.075 at low temperatures and paramagnetic semiconductor above the Curie temperature Tc. The magnitude of the saturation magnetization Ms and the ferromagnetic phase are reduced with increasing δ. A ferromagnetic insulating state below 115K is observed for δ = 0.1 sample. It seems to be due to an ordering of Mn3+ and Mn4+ species on the manganese lattice
[en] The compound Fe2Mn2O7 was prepared using ceramic method Fe2O3 and MnO2 as a precursor. It was crystallized in pyrochlore oxides type monoclinic structure in the P2/M space group. Concerning the magnetic study, they showed that the compound undergoes a ferromagnetic (FM) transition near 68 K. As for the Arrott’s plots, they revealed a second-order phase transition. The variation of the applied magnetic field revealed a magnetocaloric effect that is manifested by a maximum variation of the magnetic entropy of 1 J/kgK for a field change of 5 T, with a cooling power of 63J/kg.
[en] Magnetocaloric effect and order of transition in (La1-xNdx)2/3(Ca1-ySry)1/3MnO3, prepared by conventional solid-state reaction, have been investigated. Using Banerjee criterion, we demonstrate first-order transition for (J1) and (J2) as well as second-order transition for (J3), (J4), and (J5) samples. The ΔSMmax is ranging between 9.18 Jkg-1 K-1 and 4.87 when Nd and Sr content changes leading to relative cooling power (RCP) varying between 330 and 229.35 J/kg. Both ΔSMmax and the RCP are found sensitive to the disorder σ2. The universal behavior obtained from ΔS variation curves confirmed the first-order transition for (J1) and (J2) samples and second-order transition for (J3), (J4), and (J5) samples obtained by Banerjee criterion. All samples with second-order phase transition exhibit inhomogeneous character estimated from local exponent n. (orig.)
[en] Highlights: • Magnetic entropy change of samples was investigated at low temperatures. • These samples show second-order transition phase. • A discord between experimental magnetic entropy change and Landau theory. Magnetic entropy change of Dy0.5(Sr1−xCax)0.5MnO3 nanoparticles (0 ≤ x ≤ 0.3) was analyzed at low temperatures to investigate the magnetic refrigeration as a promising tool for hydrogen liquefaction. These samples depict interesting values of maximum magnetic entropy change and large relative cooling power, especially for x = 0.3 sample (about 169 J/Kg). It could be a promising candidate for magnetic refrigeration at cryogenic temperatures. Landau theory presents a discord between the experimental magnetic entropy change and the theoretical one. This disagreement is tending to be in accordance as Ca substitution is increasing and also with augmenting the applied magnetic field.
[en] The article titled “Strontium-substituted La0.75Ba0.25−xSrxFeO3 (x = 0.05, 0.10 and 0.15) perovskite: dielectric and electrical studies”, written by F. B. Abdallah, A. Benali, S. Azizi, M. Triki, E. Dhahri, M. P. F. Graça, M. A. Valente, was originally published electronically on the publisher's internet portal (currently SpringerLink) on March 2019 with open access.