Effect of substrate temperature on electrical and magnetic properties of epitaxial La1−x Pb x MnO3 films
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Metal–insulator transition
Transition temperature
Manganite
The structural, magnetic, and transport properties of a mono-layered manganite $La_{0.7}Sr_{1.3}MnO_{4+{\delta}}$ were investigated using variable temperature neutron powder diffraction as well as magnetization and transport measurements. The compound adopts the tetragonal I4/mmm symmetry and exhibits no magnetic reflection in the temperature region of 10 K ≤ T ≤ 300 K. A weak ferromagnetic (FM) transition occurs about 130 K, which almost coincides with the onset of a metal-insulator (M-I) transition. Extra oxygen that occupies the interstitial site between the [(La,Sr)O] layers makes the spacing between the [MnO₂] layers shorten, which enhances the inter-layer coupling and eventually leads to the M-I transition. We also found negative magneto resistance (MR) below the M-I transition temperature, which can be understood on the basis of the percolative transport via FM metallic domains in the antiferromagnetic (AFM) insulating matrix.
Manganite
Metal–insulator transition
Colossal Magnetoresistance
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In this paper, we report the results of the investigations on the transport properties performed across the manganite–manganite interface in the LaMnO3−δ/La0.7Ca0.3MnO3/LaAlO3 (LMO/LCMO/LAO) heterostructure.
Manganite
Interface (matter)
Lanthanum manganite
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Conductivity data for La2-2xSr1+2xMn2O7 (x=0.6) show a first-order transition from an orbital- or charge-ordered insulator to a metal as the temperature falls below similar to 160 K. The change in conductivity is 100 times larger than that seen previously in any single-phase manganite in zero field. The metallic low-temperature state is similar to x=0.58, but x=0.58 shows no evidence of orbital or charge order. This result supports a conclusion that strongly coupled magnetic-conductive transitions are first order.
Manganite
Metal–insulator transition
Charge ordering
Colossal Magnetoresistance
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We observed a large HEMD effect in the bilayer manganite (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$, a direct consequence of field driven spin-glass insulator to ferromagnetic metal transition. The remnants of the transition can be used to achieve dielectric contrast at room temperature. This discovery suggests that electronic mechanisms such as the metal-insulator transition, charge ordering, and orbital ordering can be exploited to give substantial dielectric contrast in other materials.
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The effects of substitution of Ca by Ba in La1−xCaxMnO3 (LCMO) with x<0.5 were investigated systematically in order to clarify the role of the size of the A cations. As for the La1−x(Ba–Ca)xMnO3 (LBCMO) films of ferromagnetic metallic (FMM) region (x=0.2; 0.3; and 0.4), by doping Ba, the ferromagnetic transition temperature (TC) and the insulator-to-metal (IM) transition temperature (TIM) were improved about 30–60 K, compared with those of LCMO thin films with the same ratio of Mn3+:Mn4+. Especially, La0.7Ba0.1Ca0.2MnO3 thin films have an anomalously high TC (about room temperature) and a TIM of 275 K under zero field. In the ferromagnetic insulating (FMI) region (x=0.15; 0.1), the Ba doping enables the IM transition and remarkably heightens the TC as well. The phase diagram shows that in the slightly doped region (x<0.5), Ba doping has made the FMM phase significantly expanded.
Metal–insulator transition
Transition temperature
Colossal Magnetoresistance
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Manganite
Metal–insulator transition
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We report on the role of oxygen content alone on structural and transport properties of La0.65Sr0.35MnO3−δ (LSMO) thin films. Identical films were deposited side-by-side during a single deposition run and subsequently post-annealed separately in vacuum to systematically vary the oxygen content. All films remained coherently strained to the SrTiO3 substrate, with no broadening of rocking curve widths after post-anneal. As oxygen content decreases, the LSMO unit cell expands while the metal-insulator transition temperature TMI decreases. A linear correlation between the out-of-plane lattice parameter and the metal-insulator transition temperature was observed.
Manganite
Metal–insulator transition
Transition temperature
Lattice constant
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Manganite
Atmospheric temperature range
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To explore the mechanisms behind the metal-insulator transition and charge transport in high temperature superconducting cuprates, a systematic study on the Bi1.7Pb0.4Sr2Ca1.1Cu2.1O8+δ compound was made by adding the rare-earth dysprosium at stoichiometric amounts (x) of 0.5≤x≤1. Phase analysis, determination of lattice parameters, microstructure analysis, and elemental analysis were carried out to evaluate the relative performance of the samples prepared by the solid state synthesis route. Charge transport in the insulating and superconducting samples were analyzed through resistivity measurements at (64–300 K). It is found that the x=0.5 sample is superconducting with a critical transition temperature of 94.8 K while for the samples with x>0.5 superconductivity is suppressed, along with an increase in their normal state resistivities. A metal-insulator transition is found to take place around 0.5<x≤6. A detailed analysis of the experimental data shows that the hole filling and disorder, induced by change in charge carrier concentration, lead to a metal-insulator transition in the present system. Also the conductivity of the semiconducting samples (x>0.5) at lower temperature is due to the two-dimensional variable range hopping mechanism of charge carriers between the spatially localized states.
Dysprosium
Metal–insulator transition
Transition temperature
Charge carrier
Variable-range hopping
Stoichiometry
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1953)
To ascertain the origin of manganese minerals, I studied the thermal differential curves and X-ray properties (powder method) of manganese oxide minerals (psilomelane, pyrolusite and manganite etc.), and following results were obtained. Psilomelane, pyrolusite and manganite denote different dissociations for a temperature. (Each thermal differential curves also are different.) At about 600°C, psilomelane was altered to manganite, and pyrolusite to manganite, but manganite was not changed. Moreover, when psilomelane, pyrolusite and manganite were treated in a water for 200 hours, manganite was altered to psilomelane, and pyrolusite to psilomelane, and psilomelane was not changed. From above results, psilomelane, pyrolusite and manganite were altered each other by the influence of temperature or water, and they will be occurred in nature in altered forms through the complicated processes.
Pyrolusite
Manganite
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