Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Microchemical investigation of medicinal plants. V

Summary The spectral analysis of the yellow compound isolated from the seeds ofC. Bignonioides was carried out to further investigate its structure. The presence of two methoxyl groups, two hydroxyl groups, and an ,-unsaturated carbonyl is firmly established. It is not possible at this time to substantially confirm whether the carbonyl is an aromatic aldehyde or a six-membered ring ketone. The molecular formula, C₁₇H₁₄O₆ (11 sites of unsaturation and/or rings), is established. The compound does not contain any methyl or methylene groups. The location of one methoxyl and one hydroxyl closer to an electronegative group (i. e. a furanoic oxygen) is indicated. The hydroxyl groups are not located ortho to the carbonyl.The compound has a polynuclear aromatic structure. The evidence indicates one ring is 1,2,3,4-tetra substituted. Another ring may be 1,2,3,5-tetrasubstituted or 1,3,5-trisubstituted. A heteroaromatic group (e. g. furan) may also be present.Further work is in progress to elucidate the structure of the compound.

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Zusammenfassung Die Spektralanalyse der gelben, aus Catalpasamen isolierten Verbindung wurde zwecks weiterer Untersuchung ihrer Struktur durchgeführt. Die Anwesenheit zweier Methoxylgruppen, zweier Hydroxylgruppen und einer,-ungesättigten Carbonylgruppe wurde sichergestellt. Bis jetzt ist nicht zu entscheiden, ob letztere einer aromatischen Aldehydgruppe oder einem sechsgliedrigen cyklischen Keton zugehört. Die Summenformel C₁₇H₁₄O₆ mit elf ungesättigten Bindungen und/oder Ringen wurde nachgewiesen. Die Verbindung enthält keine Methyl- oder Methylengruppen. Die Lokalisation einer Methoxyl- und einer Hydroxylgruppe in der Nähe einer elektronegativen Gruppe (das heißt, eines furanoiden Sauerstoffs) ist erkennbar. Die Hydroxylgruppen stehen zur Carbonylgruppe nicht ino-Stellung.Die Verbindung hat polynukleare aromatische Struktur. Ein Ring ist in den Stellungen 1, 2, 3 und 4 substituiert, ein weiterer in den Stellungen 1, 2, 3 und 5 oder nur in 1, 3 und 5. Eine heterocyklische Gruppe (z. B. Furan) dürfte anwesend sein. Die Untersuchungen werden fortgesetzt.

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For Part IV see Mikrcohim. Acta [Wien]1968, 1085.