Electrical Transport Properties Of La0 Research Articles

Fe3O4 Segregation and Transport Properties ofLa0.67Ca0.33MnO3

Effect of Fe3O4 segregation at grain boundaries on theelectrical transport and magnetic properties ofLa0.67Ca0.33MnO3 is investigated. The experimentalresults show that the Fe3O4 segregation not only shiftsthe paramagnetic–ferromagnetic transition temperature ofLa0.67Ca0.33MnO3 to a lower temperature region butalso induces a new transition in a lower temperature region. Meanwhile,the transition processes observed in both the resistivity andmagnetization curves are obviously widened. Compared to pureLa0.67Ca0.33MnO3, we assume that theFe3O4 segregation level at the grain boundaries canmodify the electrical transport and magnetic properties ofLa0.67Ca0.33MnO3.

Magnetic and electrical transport properties of La0.67Ca0.33MnO3 (LCMO): xSiCN composites

The magnetic and electrical transport properties of La0.67Ca0.33MnO3 (LCMO): xSiCN (x=0–40 vol %) composites, synthesized by mechanical mixing of citrate gel derived LCMO and polymer derived ceramics SiCN, have been investigated as a function of composition. The ability of SiCN to behave as a sintering additive leads to interesting magnetic and electrical properties. Si+4, being strongly favored for tetrahedral coordination, cannot enter the perovskite lattice. Saturation moment, MS of 68 emu/gm at 5 K and at 5 kOe field of pure LCMO shifts to 79 emu/gm in the sample with x=0.05 and then decreases monotonically as x increases further. The lower MS, TC and high electrical resistivity of the sample with x=0, compared to those which have been reported in the literature, is due to small particle size in nm range. SiCN as a sintering aid increases the particle size of LCMO to 1–2 μm for x=0.10. Three orders of magnitude change in electrical resistivity (204 Ω cm for x=0;0.5 Ω cm for x=0.05) is explained on the basis of the difference in the mobility of the charge carriers, by fitting the experimental transport data with a correlated polaron hopping model.

Temperature sintering effects on the magnetic, electrical and transport properties ofLa0.67Sr0.33MnO3/Nd0.67Sr0.33MnO3 composites

The microstructure, magnetic and electrical transport properties ofLa0.67Sr0.33MnO3/Nd0.67Sr0.33MnO3 composites are studied as a function of sintering temperature. At900 °C, the intergrain exchange couplings between the adjacent particles give rise to an increase inresistance. Raising the sintering temperature induces the formation of an interfacial phase near theLa0.67Sr0.33MnO3 and Nd0.67Sr0.33MnO3 grain boundaries as indicated in the XRD pattern and SEM image. At1100 °C, the formation of interfacial phases near the grain boundaries enhances the conductivity in thecomposite. Broad magnetoresistance across room temperature is observed in a composite sintered at1300 °C. This observation may be ascribed to the coexistence of multiphase in the composite whichleads to a decrease in resistance. The results suggest that sintering temperaturehas a prominent effect on the properties of the grain boundary, which plays animportant role in determining the electrical transport behaviour of the composites.

Magnetic State of Ba-Doped Manganites Depending on the Oxygen Vacancy Concentration

Magnetization and electrical transport properties of La0.60Ba0.40MnO3—γ (0 ≤ γ ≤ 0.20) anion-deficient manganites have been studied. Magnetic ordering temperature decreases insignificantly with γ in contrast to spontaneous magnetization. Ferromagnetic metallic ground state of stoichiometric samples (γ = 0) is destroyed gradually with increasing oxygen vacancy concentration (to γ = 0.20). It is shown that the long-range ferromagnetic order remains for γ ≤ 0.10 while the cluster spin glass properties appear for 0.10 < γ ≤ 0.20 with temperature of cluster moment freezing of 40 K. Electrical resistivity behavior of the samples with 0 ≤ γ ≤ 0.10 correlates with magnetization. Below the magnetic ordering temperature the resistivity becomes of metallic type and a peak of magnitoresistance is observed. The strongly reduced samples (0.10 < γ ≤ 0.20) have the activated type resistivity and exhibit a large magnetoresistance below the temperature at which the spontaneous magnetization occurs. For the explanation of the obtained results it is assumed that both the Mn3+–O–Mn3+ and the Mn3+–O–Mn4+ magnetic interactions become negative near the oxygen vacancies. The magnetic state of the anion-deficient samples is interpreted basing on the superexchange interaction model.

Cu Doping as a Tool for Understanding CMR

Doping at the Mn-site in CMR manganate-based perovskites has been shown to affect strongly the physical properties of those compounds. We study here the effect of copper substitution in the low doping range on the electrical transport properties of La0.7Ca0.3MnO3. It turns out that the transition temperature decrease observed in doped samples can be drastically reduced by addition of silicon dioxide SiO2. It is shown that copper is trapped in a secondary phase composed of La,Ca,Si,Cu and O. The resultant Mn-site vacancies appear to be less detrimental to the electronic conduction than the likely antiferromagnetic clusters induced by the copper ions in the Mn-O network.

Effect of Oxygen Content on the Electrical Transport Properties of La0.4Ca0.6MnO3?y

The effect of oxygen content on the electrical transport properties of La0.4Ca0.6MnO3—y was studied. Upon decreasing oxygen content, the lattice parameters a, b and c of the samples increase and the electrical resistivity of the samples also increases abruptly, contradicting what is expected in terms of Mn4+/Mn3+ ratio. This work suggests that other factors rather than the ratio of Mn4+/Mn3+ may play a role in determining the properties of La0.4Ca0.6MnO3—y with less oxygen contents.

Effect of Oxygen Content on the Electrical Transport Properties of La0.4Ca0.6MnO3y

Effect of Oxygen Content on the Electrical Transport Properties of La0.4Ca0.6MnO3y

Epitaxial growth and electrical transport properties of La0.5Sr0.5Co03 thin films prepared by pulsed laser deposition

Epitaxial growth of the La0.5Sr0.5 3(LO) thin films has been realized on Lin3, SrTiC3 and MgO substrates by pulsed laser deposition. The epitaxial growth behavior and the electrical transport properties of these films were studied systematically. The temperature dependencies of the resistivity of the film have been determined. Studies indicate that close dependencies exist between the crystal structures and the electrical transport properties of the epitaxial LSCO films, and that the epitaxial thin films are of low resistivity and metallic conductive features. The epitaxial films deposited on the LaA103 substrates at about 700 °C possess the optimal properties compared with the others. Discussions of the dependencies and the mechanisms of the epitaxial structures on the electrical transport properties of the LSCO films have been made.