Fluctuation conductivity in superconducting MgB2

According to the crystal structure of MgB₂ and band structure calculations, quasi-two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical-field and resistance measurements of 5.6-μm-thick MgB₂ films grown on a sapphire single-crystal substrate. Resistivity measurements yield a temperature dependence of the fluctuation conductivity above the critical temperature, which agrees with the Aslamazov-Larkin and Maki-Thompson theory of fluctuations in layered superconductors, indicating a quasi-two-dimensional nucleation of superconductivity in MgB₂.     

The structure of 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one

Crystal and molecular structure of 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one as a product of the benzoylation of 1-phenyl-3-benzoylaminopyrazol-2-in-5-one was characterised by X-ray single crystal diffraction. It is shown that 1-phenyl-3-benzoylamino-4-benzoylpyrazol-2-in-5-one exists in the solid phase in an NH-tautomeric form, which is stabilised by two intramolecular hydrogen bonds and one intermolecular bond with the solvate dioxane molecule, the latter being used as a solvent for recrystallisation.     

EPR study of ordered Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-based aerogel

Samples of oriented aerogel based on aluminum oxide are studied by the electron paramagnetic resonance (EPR) technique under steady-state and pulse conditions. At least two types of paramagnetic centers interacting with Al nuclei on the surface of aerogel are revealed. Their spectra are characterized by the presence or absence of superhyperfine structure in the EPR spectra, respectively. The X-ray irradiation at room temperature gives rise to the formation of additional long-lived paramagnetic centers of the second kind. Their characteristic decay times for the “fast” and “slow” processes are determined. The interaction of induced paramagnetic centers with protons located on the surface of aerogel is revealed.     

2-{(4a′S,6a′S,10a′R,10b′R)-Octahydrospiro[1,3-dioxolane-2,2′-pyrano[2,3-c]chromen]-6a′(1′H)-yloxy}ethanol in the Synthesis of (2S)- and (2R)-Dodecane-1,2-diols

Russian Journal of Organic Chemistry - Michael adduct of levoglucosenone and cyclohexanone, 1,6-anhydro-3,4-dideoxy-4-C-(2-oxocyclohexan-1-yl)-β-D-erythrohexo-2-ulose, was treated with...     

Synthesis of Nonano-9-lactones Fused to a Pyran Ring Containing a Dichloromethylene Substituent

Russian Journal of Organic Chemistry - The Michael adducts of levoglucosenone and cyclohexanone were used to develop a rapid synthesis of nonano-9-lactones fused to a pyran ring containing a...     

Experimental observation of the spin screening effect in superconductor/ferromagnet thin film heterostructures

When studying the nuclear magnetic resonance (NMR) of ⁵¹V nuclei in superconductor/ferromagnet thin film heterostructures, anomalous behavior of the NMR signal was observed. This effect was manifested as a systematic distortion of the high-field wing of the resonance line. We consider this to be the first experimental evidence for penetration of ferromagnetism into a superconductor.     

Specific features of depth distribution profiles of implanted cobalt ions in rutile TiO<Subscript>2</Subscript>

This paper reports on the results of the calculation of the depth distribution profiles of the concentration of the impurity implanted into an anisotropic crystalline material. The sputtering of the irradiated material, fast one-dimensional diffusion of the impurity along structural channels, and accumulation of the implanted impurity at different depths have been taken into account. The results of the calculations have been compared with the experimental distribution profiles of cobalt ions implanted into the crystal structure of rutile TiO₂ along and across structural channels at different temperatures of the irradiated substrate. A comparison of the model and experimental profiles has made it possible to evaluate the precipitation rate of cobalt in the TiO₂ matrix on different precipitation centers. A model has been proposed for explaining the unusual shift in the peak of the concentration distribution of implanted ions deep into the sample with an increase in the temperature of the irradiated substrate. The model has allowed one to separate the contributions from different phases of the impurity (nanoparticles and solid solution) to the magnetism of the Co: TiO₂ system.     

Synthesis of Thin Niobium Films on Silicon and Study of Their Superconducting Properties in the Dimensional Crossover Region

Technical Physics - Niobium films with a thickness of 4–100 nm are synthesized on a silicon substrate under ultrahigh vacuum conditions. Measurements of the electrical resistance show a high...     

Effect of phase transitions of helium-3 in pores of wood carbonizate on the spin kinetics of 3He nuclei

The time of the nuclear magnetic relaxation of ³He gas in pores of Astronium carbonizate powder is studied as a function of gas pressure. Using the results of the measurements of the spin-echo amplitude, the dependences of the rates of spin-lattice and spin-spin relaxations on the number of helium atoms on the surface, in pores, and in the interparticle space of carbonizate powder have been determined. Analysis of the relaxation rates allows the identification of three possible basic phases of ³He in the system under consideration: solid film, gas phase, and liquid. Moreover, the character of spin kinetics in transitions between these phases has been determined.