Measurement of the asymmetry in the decay Omega+-->LamdaKappa+-->rhopi+Kappa+

The asymmetry in the rho angular distribution in the sequential decay Omega+-->LamdaKappa+-->rhopi+Kappa+. has been measured to be alphaOmegaalphaLamda=[+1.16+/-0.18(stat)+/-0.17(syst)]x10(-2) using 1.89x10(6) unpolarized Omega+ decays recorded by the HyperCP (E871) experiment at Fermilab. Using the known value of alphaLamda, and assuming that alphaLamda=-alphaLamda, alphaOmega=[-1.81+/-0.28(stat)+/-0.26(syst)]x10(-2). A comparison between this measurement of alphaOmegaalphaLamda and recent measurements of alphaOmegaalphaLamda made by HyperCP shows no evidence of a violation of CP symmetry.     

Multiferroic behavior in silicate glass nanocomposite having a core–shell microstructure

Nanosized iron core and barium titanate shell microstructure was generated within a silicate glass of composition 23.1 Na₂O, 23.1 BaO, 23.0 TiO₂, 7.6 B₂O₃, 5.8 Fe₂O₃, 17.4 SiO₂ by first reducing it at 893 K for ½ h and then subjecting it to heat treatment at 759 K for 4 h. Transmission electron microscopy showed the composite particles to have a mean diameter of 3.9 nm. The nanocomposite exhibited both ferroelectric and ferromagnetic behavior. The dielectric constant peak was not prominent because of a small thickness of the barium titanate phase. The magnetic hysteresis loop showed an asymmetric behavior giving rise to a small exchange bias field. This is believed to arise due to exchange interaction between the ferromagnetic iron core and the thin layer of Fe₃O₄ on the core surface with a spin glass-like behavior. The magnetization under zero-field cooled (ZFC) and field cooled (FC) conditions indicated superparamagnetic behavior at temperatures higher than 300 K. The optical absorption spectra exhibited a peak at around 325 nm. This was analyzed satisfactorily on the basis of a metal core–oxide shell nanoconfiguration. The extracted values of metal core conductivity showed a metal insulator transition for iron core diameters less than 2.4 nm. The present synthesis approach will lead to newer multiferroic nanocomposites and glasses with multifunctionalities.     

Synthesis of two-dimensional metallic silver using sodium beta-alumina crystal channels

Sodium beta-alumina (β-NaAl₁₁0₁₇) crystals were grown within a gel containing Na₂O and Al₂O₃. The glass–crystal composite was put through a Na⁺ ? Ag⁺ ion-exchange reaction. The ion-exchanged glass–crystal was then subjected to an electrodeposition process. Nanosheets of metallic silver were found to have grown within the β-NaAl₁₁0₁₇ channels which usually contain the mobile sodium ions. The DC electrical resistance of the composites was caused due to charge transport in the two-dimensional crystal planes. The average silver layer thickness was ～0.6 nm and the interlayer separation ～1.13 nm.     

Effect of organized assemblies II. Environmental effect on the pK of (o/p) hydroxybenzylidene-(4/6)-nitro-2-aminobenzothiazoles

The dissociation constants (pK's) of aldimines, (o/p) hydroxybenzylidene-(4/6)-nitro-2-aminobenzothiazoles, have been determined spectrophotometrically in the absence and presence of ionic and nonionic surfactant assemblies at 27 degrees C. Substantial shifts in the pK's of the aldimines has been observed in the presence of the organized assemblies compared to water. The results have been attributed to the surface charge of the micelle, the effective hydrophobicity of the surfactants, and field and resonance effects due to NO(2) group substitution. Surfactant assemblies are found to have randomly arranged hydrophobic chains leading to exposure of some of the hydrocarbon chain segments to bulk water. The results also support the presence of intramolecular H-bonding in the o-hydroxybenzylidene-(4/6)-nitro-2-aminobenzothiazoles.     

Preparation of nanocrystalline MnFe2O4 by doping with Ti ions using solid-state reaction route

Nanostructured manganese ferrites (MnFe₂O₄) with diameters in the range of 45–30 nm were synthesized by Ti⁴⁺ ion doping, using conventional solid-state reaction route. The substitution of Ti⁴⁺ ions created vacancies at Mn²⁺ sites and the coupling of ferrimagnetically active oxygen polyhedra was broken. This created nanoscale regions of ferrites. A reduction of magnetization for decreasing particle size was observed. Coercivity showed an increasing trend. This was explained as arising due to multidomain/monodomain magnetic behaviour of magnetic nanoparticles. DC resistivities of the doped specimens indicated the presence of an interfacial amorphous phase formed by the nanoparticles. Zero-field cooled and field-cooled curves from 30 nm sized particles showed a peak at T_B (∼125 K), typical of superparamagnetic blocking temperature.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

Mössbauer effect studies of alkali borate glasses

Mössbauer studies of a large number of glass samples prepared with alkali oxides in the region of glass formation are reported. Some representative samples are studied in the temperature range 85–500 K. The following glass systems are studied.

Room-temperature isomer shift values decrease gradually with the addition of alkali oxide and the values fall sharply for alkali content higher than 22 mol%. We conclude that iron is in the ferric state and that the oxygen polyhedra of iron changes from octahedral to tetrahedral. The structural change results from the fact that the alkali introduces an extra non-bridging oxygen ion. The size of the alkali cation introduced into the glass has considerable influence on the isomer shift values of iron. In fact, the polarizing power decreases in the order LiNaK, hence the s-character of the FeO bond increases in the order LiNaK. Addition of Al₂O₃ has no effect on the isomer shift values of iron, showing that aluminium ions occupy network-forming positions.For some representative samples the second-order Doppler effect was studied as a function of temperature in the range 85–500 K. The thermal red shifts due to second-order Doppler effect are used to estimate the local specific heats of ferric ion in the glass system. The quadrupole splitting has weak temperature dependence, showing that Fe³⁺ is in a high-spin state.