The spin-wave resonance spectrum and the structure of cermet Fe - SiO films

The results of electron-microscopic investigation of the structure and spin-wave resonance of thin ferromagnetic Fe_100-x(SiO)_x films are presented in the paper. The correlation radii of fluctuations of the exchange interaction parameter are determined from the analysis of the experimental results of spin-wave resonance. These radii are compared with characteristic sizes of the structural clusters in the films.     

Mechanisms of dissipation in a Josephson medium based on a high-temperature superconductor in a magnetic field

This paper reports on the results of an investigation into the influence of magnetic fields (0–60 kOe) on the temperature dependences of the electrical resistance R(T) of the Y_3/4Lu_1/4Ba₂Cu₃O₇ + CuO composites. The structure of these composites is considered to be a network of tunnel-type Josephson junctions in which a nonsuperconducting component (CuO) forms boundaries (barriers) between high-temperature superconducting crystallites. The temperature dependence R(T) of the composites has two steps characteristic of granular superconductors: (i) an abrupt change in the electrical resistance at the critical temperature of high-temperature superconducting crystallites and (ii) a smooth transition to the superconducting state under the influence of the boundaries between the crystallites. The experimental dependences R(T) are analyzed within the Ambegaokar-Halperin model of thermal fluctuations in Josephson junctions and the flux creep model. An increase in the magnetic field leads to a crossover from the Ambegaokar-Halperin mechanism to the flux creep mechanism. The temperature dependences R(T) in the range of weak magnetic fields (from 0 to 10² Oe) are adequately described by the relationship following from the Ambegaokar-Halperin model. In the range of strong magnetic fields (from 10³ to 6 × 10⁴ Oe), the dissipation obeys the Arrhenius law R ～ exp(?U(H)/T)], which is characteristic of the flux creep model with a temperature-independent pinning energy U(H). The effective Josephson coupling energies and the pinning energies corresponding to the Ambegaokar-Halperin and flux creep mechanisms are determined.     

Interrelation of anisotropy of magnetic properties and magnetodielectric effect in a Cu<Subscript>3</Subscript>B<Subscript>2</Subscript>O<Subscript>6</Subscript> single crystal

The effect of an external magnetic field on permittivity has been studied in a Cu₃B₂O₆ single crystal with a layered structure in the direction perpendicular to layers (bc-planes). It has been found that the appreciable magnetodielectric effect in the temperature range below the Néel temperature (≈10 K) takes place only at one magnetic field orientation H and one crystallographic direction, i.e., H || b. Such “selectivity” of the magnetodielectric effect correlates with the anisotropic behavior of magnetic properties of the crystal.     

Pentapeptide analogs of somatostatin containing a thiazolidine fragment: synthesis and cytotoxic activity

Russian Chemical Bulletin - Pentapeptide analogs of somatostatin containing an (R)-1,3-thiazolidine fragment (Thz) of the general formula...     

Magnetic properties of Fe<Subscript>3</Subscript>C ferromagnetic nanoparticles encapsulated in carbon nanotubes

The low-temperature dependences of magnetic characteristics (namely, the coercive force H _c , the remanent magnetization M _r , local magnetic anisotropy fields H _a, and the saturation magnetization M _s ) determined from the irreversible and reversible parts of the magnetization curves for Fe₃C ferromagnetic nanoparticles encapsulated in carbon nanotubes are investigated experimentally. The behavior of the temperature dependences of the coercive force H _c (T) and the remanent magnetization M _r (T) indicates a single-domain structure of the particles under study and makes it possible to estimate their blocking temperature T _B = 420–450 K. It is found that the saturation magnetization M _s and the local magnetic anisotropy field H _a vary with temperature as ～T ^5/2.     

Features of the structure, microstructure, and magnetic properties of manganese-aluminum spinels obtained in various thermal treatment conditions

The structural, microstructural, and magnetic properties of aluminum-manganese oxide in the ratio Mn: Al = 1: 1 in the well-crystallized and nanoheterogeneous states have been investigated. This oxide is obtained under various thermal treatment conditions and at different partial pressures of oxygen. The composition and cation distribution of the manganese and aluminum ions in spinel sites are determined. It is shown that the studied compound is a ferrimagnet with the Curie point T _C ≈ 26 K.     

Mechanism of formation of a negative magnetoresistance region in granular high-temperature superconductors

The field dependences of the magnetoresistance of Bi_1.8Pb_0.3Sr_1.9Ca₂Cu₃O _x samples with different densities, which have a foam microstructure and exhibit different diamagnetic responses, were studied at 77.4 K to identify the mechanism responsible for the formation of a negative magnetoresistance region in granular high-temperature superconductors. A region with negative magnetoresistance was found to exist in samples with magnetizations highest in absolute magnitude. This behavior finds a reasonable interpretation as due to the effect exerted by dipole moments of high-temperature superconductor grains on the effective intergranular field. The strength of this effective field has been estimated.     

Magnetic and resonance properties of ferrihydrite nanoparticles doped with cobalt

Powders of undoped ferrihydrite nanoparticles and ferrihydrite nanoparticles doped with cobalt in the ratio of 5: 1 have been prepared by hydrolysis of 3d-metal salts. It has been shown using Mössbauer spectroscopy that cobalt is uniformly distributed over characteristic crystal-chemical positions of iron ions. The blocking temperatures of ferrihydrite nanoparticles have been determined. The nanoparticle sizes, magnetizations, surface anisotropy constants, and bulk anisotropy constants have been estimated. The doping of ferrihydrite nanoparticles with cobalt leads to a significant increase in the anisotropy constant of a nanoparticle and to the formation of surface rotational anisotropy with the surface anisotropy constant K _u = 1.6 × 10^–3 erg/cm².     

A shortened,protecting group free,synthesis of the anti-wrinkle venom analogue Syn-Ake® exploiting an optimized Hofmann-type rearrangement

An unusual five-step synthesis of H-β-Ala-Pro-DabNHBz diacetate (a muscular nicotinic acetylcholine receptor antagonist) has been delineated through Hofmann-type rearrangement as a final step to build the target skeleton. The synthesis has been carried out using a protecting group free strategy and employed readily available reagents as the starting materials.     

Effect of thermal fluctuations on the resistive properties of HTSC+CuO composites

The effect of thermally activated phase slippage (TAPS) on the resistive properties of Y_3/4Lu_1/4Ba₂Cu₃O₇+O₇ composites has been studied. The experimental temperature dependences of the electrical resistance are described in terms of the TAPS mechanism using the temperature dependences of the tunnel-junction critical current. Fiz. Tverd. Tela (St. Petersburg) 39, 1956–1957 (November 1997)