Quantitative interpretation of EELS and REELS spectra

We analyze the effects of the background velocity and the initial magnetic field correlations, and viscosities on the turbulent dynamo and the -effect. We calculate the -coefficients for arbitrary magnetic and fluid viscosities, background velocity and the initial magnetic field correlations. We explicitly demonstrate that the general features of the initial growth and late-time saturation of the magnetic fields due to the non-linear feedback are qualitatively independent of these correlations. We also examine the hydrodynamic limit of the magnetic field growth in a renormalization group framework and discuss the possibilities of suppression of the dynamo growth below a critical rotation. We demonstrate that for Kolmogorov-(K41) type of spectra the Ekman number for dynamo growth to occur.Received: 14 November 2003, Published online: 20 April 2004PACS: 47.65. + a Magnetohydrodynamics and electrohydrodynamics - 91.25.Cw Origins and models of the magnetic field; dynamo theories     

Peculiarities of the magnetic structure of the cryogenic permanent magnet Tb<Subscript>3</Subscript>Co

The magnetic state of the Tb₃Co compound with orthorhombic structure has been investigated by measuring the magnetization in static and pulsed magnetic fields and using neutron diffraction analysis. It is shown that the antiferromagnetic modulated structure, arising in this material at T < T _N = 82 K, passes upon cooling below T _t ≈ 72 K to an incommensurate magnetic structure with a ferromagnetic component along the c axis.     

Applying invariant embedding methods to the theory of thin film sputtering by light-ion bombardment

An analytical solution to the problem of energy spectra of sputtered atoms under light-ion bombardment of plane-parallel layer is obtained. The proposed theory is based on the invariant embedding principle applied in combination with the discrete flow method. This approach provides absolutely precise fulfillment of the boundary conditions of the Boltzmann kinetic equation. In addition, both reverse sputtering and strike sputtering can be described. The proposed method of solving plane-parallel layer problems makes it possible to approach the study of sputtering spectra of multilayer structures. In addition, a number of features peculiar to light-ion sputtering only can be considered.     

Conductivity jumps and low-temperature magnetoresistance in the new semiconducting perovskites La1− x BixMnO3+δ

Abrupt jumps are observed on the temperature dependences of the electrical conductivity of La_{1− x} Bi_xMnO_3+δ (0.1<x<0.7) and La_0.3Bi_0.7Na_0.1MnO_3+δ ceramics. The temperatures at which the jumps take place can be reduced by several degrees by applying an external magnetic field of 15 kOe. It can be seen from the magnetization data that the poorly conducting low-temperature phase is not antiferromagnetic (it is likely ferromagnetic) and hence the real-space charge ordering mechanism is not sufficient for explaining the experimental results. An interpretation in terms of magnetic phase nonuniformity is proposed. All the samples studied exhibit high low-temperature magnetoresistance. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 250–253 (25 August 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Dielectric polarization of bismuth titanate,Bi2O3·3TiO2

Experimental data describing the dielectric polarization of polycrystalline bismuth titanate, Bi₂O₃·3TiO₂, is cited, and the physical nature of its polarization discussed. We conclude that Bi₂O₃·3TiO₂ at temperatures equal to or lower than that of liquid nitrogen is a ferroelectric, while at considerably higher temperatures it is a normal relaxation process dielectric.     

The PLM Plasma Device for Tests of Tungsten with Powerful Stationary Heat Plasma Loads

The PLM plasma device for plasma testing of refractory metals and materials of a fusion reactor (like the fusion neutron source and DEMO) within the framework of the domestic fusion program and the ITER project was constructed at the National Research University Moscow Power Engineering Institute in 2017. The device is a linear trap with a multicusp magnetic confinement of plasma. At the facility, tests of tungsten and experiments are being carried out aimed at creating a technology for producing a highly porous surface structure of refractory metals such as tungsten and molybdenum, including those with a fuzzy surface structure with the size of elements of the structure up to 50 nm.     

Nuclear57Fe relaxation in Fe2+-containing NiFe2O4 and CoFe2O4 single crystals

Spin-lattice (T ₁) and spin-spin (T ₂) relaxation times of ⁵⁷Fe nuclei in the single-crystal NiFe₂O₄ and CoFe₂O₄ ferrites containing Fe²⁺ ions have been studied in the temperature range of 4.2–100 K by a spin-echo technique. The peaks of relaxation rates T ₁ ^?1 and T ₂ ^?1 caused by the presence of Fe²⁺ ions were observed for both ferrites in the ranges 38–42 and 28–32 K, respectively. The analysis of the results obtained with invocation of the data on ferromagnetic resonance and the measurements of the temperature dependence of resistivity shows that the mechanism of nuclear relaxation responsible for “impurity” peaks and is a slow relaxation process caused by electron exchange Fe²⁺ ? Fe³⁺, characterized by a low activation energy.     

Soft X-ray absorption spectroscopy of titanium dioxide nanopowders with cobalt impurities

The charge states of the cobalt ions in TiO₂ nanopowders with the anatase lattice are studied by soft X-ray absorption spectroscopy. It is found that, at a low cobalt impurity concentration (1.8 at %), the cobalt ions with an oxidation state 2+ are mainly located in the tetrahedral (T _d ) environment of oxygen ions. Amorphous titanium dioxide exists on the sample surface before heat treatment. Annealing in vacuum or hydrogen leads to the enrichment of the nanoparticle surfaces with Co²⁺ ions, a change in the coordination of the remaining part of cobalt ions from octahedral to tetrahedral, stabilization of the anatase structure, and the disappearance of the amorphous phase. The crystal lattice of the samples with a relatively high cobalt concentration (12 at %) is distorted, and annealing does not cause the disappearance of the amorphous phase of TiO₂. Cobalt is reduced to its metallic state upon hydrogen annealing of the samples with a high cobalt concentration.