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Interface resistive switching effects in bulk manganites

100%
Belogolovskii M.
Open Physics
|
2009
|
vol. 7
|
issue 2
304-309
EN
A physical mechanism driving the resistance switching in heterocontacts, formed by a metal counterelectrode and electrically conducting bulk perovskite manganites, is discussed. The nature of the inelastic, charge-hopping transport inside insulating and strongly inhomogeneous metal/manganite interfaces is studied theoretically. Comparison with measured current-voltage characteristics for a La0.67Ca0.33MnO3/Ag heterostructure in a high-resistance state reveals the presence of one or more charge traps along a conduction path within the interface. In a low-resistance state the main charge-transferring events are direct tunneling ones. The analysis of electrical noise measurements for a La0.82Ca0.18MnO3 single crystal in three different charge-transport regimes shows scattering centers with a broad, flat spectrum of excitation states, independent of manganite electrical and/or magnetic characteristics. All of these results are consistent with an oxygen-drift model for a bistable resistance state in perovskites.
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Electrical characteristics of HTS/manganite double layers

100%
Nurgaliev T., Štrbík V., Miteva S., Blagoev B., Mateev E., Neshkov L., Beňačka Š., Chromik Š.
Open Physics
|
2007
|
vol. 5
|
issue 4
637-649
EN
Superconductor/ferromagnetic (SC/FM) Y1Ba2Cu3O7−δ /La0.7Sr0.3MnO3 (YBCO/LSMO) double layers were prepared on LaAlO3 substrates by magnetron sputtering and their electrical and microwave parameters were investigated at 77 K. In the theoretical plan, simple formulas for estimation of the sensitivity of the SC surface impedance to the concentration changes of normal charge carriers were proposed and the surface resistance R S peculiarities of both SC and FM surfaces were described. Thinner YBCO/LSMO structure was characterized by lower SC parameters and higher surface resistance R S at ∼ 4 GHz. The difference of R S of sample SC surfaces was interpreted as due to a difference between the normal charge carrier densities in these samples. R S of the FM surface was higher than that of the SC surface due to the microwave losses of the magnetic subsystem. A peak of the microwave losses, observed in the thicker double layer, was assumed to be caused by uniform FMR in the LSMO film.
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Structural and magnetic characterisation of the perovskite oxides La0.7Ca0.3−x NaxMnO3

100%
Tozri A., Bejar M., Dhahri E., Hlil E.
Open Physics
|
2009
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vol. 7
|
issue 1
89-95
EN
X-ray powder diffraction (XRD) and magnetic measurements were performed in order to investigate the effect of Na+ ion substitution for Ca2+ ions on the crystallographic structure, the character of magnetic ordering, and the effect of transition temperature in La0.7Ca0.3−x NaxMnO3 manganites series (0 ⩽ × ⩽ 0.2). All samples crystallise in an orthorhombic structure with the Pnma space group. We have found a strong dependence of structural and magnetic properties on the cation-size disorder parameter σ 2. The temperature dependence of magnetization of all samples obeys the Bloch T 3/2 law. The values of the spin wave constant at low temperature B increase with the increase of x and the Curie temperature decreases. It is concluded that the substitution of Ca by Na+ ions causes a decrease in total exchange integral Aof the samples.
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