Bulletin of the Russian Academy of Sciences: Physics最新文献

A study was made of the possibility of modifying the near-surface silicon layer before and after ion implantation, followed by pulsed light annealing, to structure the surface of the substrates to increase the efficiency of their use in solar energy. The results were compared with the data obtained on monocrystalline and implanted germanium.

The advantages and features of using a medium-field MRI system for studies of various agricultural objects are considered, a series of special sensors for optimizing such studies is developed, new methods of data processing and analysis are described, and some experimental results are presented.

The generation of the second harmonic is investigated on microperiodic nonlinear polarizability gratings photointegrated upon volumetric optical poling in aluminum and germanium silicate glasses. A comparison shows the strong impact of nitrogen, phosphorus, and rare-earth element additions. An original theory of nonlinear-frequency conversion using the current mechanism allows the characteristics and magnitudes of photointegrated nonlinearities in glasses to be estimated. A strong dependence is revealed of the efficiency of harmonic generation on the intensity of the poling radiation component, due to the possible influence of photoconductivity. This dependence must be considered when developing promising samples with photointegrated gratings.

Results are presented from investigating the structure of Mn_2.25Co_0.75BO₅ via powder neutron diffraction. Crystals of ludwigite Mn_2.25Co_0.75BO₅ are grown by flux method using a Bi₂Mo₃O₁₂-based solvent diluted with Na₂CO₃ carbonate. Boric acid ({text{H}}_{3}^{{11}}{text{B}}{{{text{O}}}_{{text{3}}}}) is used as the boron-containing reagent. Powder neutron diffraction measurements are made at a temperature of 100 K on powder prepared by grinding grown single crystals. Rietveld studies show that the grown Mn_2.25Co_0.75BO₅ crystals belong to Pbam space group. Crystallographic sites occupied by cobalt and manganese ions are identified by analyzing powder neutron diffractograms. A bottleneck regime is observed in the temperature dependence of the EPR spectra.

The viscous friction of a ferrofluid in the coaxial gap between a stationary outer nonmagnetic tube and a uniformly and rectilinearly moving inner cylindrical permanent magnet was investigated experimentally and theoretically. An analytical expression for the effective coefficient of friction was proposed within the framework of the model concepts of the Couette–Poiseuille flow profile with zero flow rate and was confirmed in a laboratory experiment.

Results are presented from studying the magnetostatic and magnetoresonant properties of a thin-film bilayer Fe₃Al/Pt structure synthesized via molecular beam epitaxy. Magnetometry and ferromagnetic resonance data indicate the four-fold in-plane magnetocrystalline anisotropy of the Fe₃Al layer. The magnetic field dependence of the voltage induced by the inverse spin Hall effect is measured under conditions of spin pumping, and the quantitative characteristic of the spin-charge transformation in platinum (the spin Hall angle) is estimated as θ_SH = 0.030 ± 0.005.

Li₃V₂(PO₄)₃-based composites as a lithium-ion battery cathode material were synthesized by the hydrothermal method with subsequent annealing in an Ar atmosphere. The as-prepared samples were characterized by X-ray diffraction analysis and electron spin resonance (ESR) methods. Based on ESR, data the quantitative estimation of V⁴⁺ content was performed. The tetravalent vanadium ions arised instead of trivalent vanadium ions due to lithium nonstoichiometry in Li₃V₂(PO₄)₃ structure. This method of identifying nonstoichiometry via ESR detection of V⁴⁺ ions is very simple and demonstrative and can be used to characterize not only as-prepared samples but also samples after multiple electrochemical cycling. This technique of the lithium nonstoichiometry detection in Li₃V₂(PO₄)₃ can be used if the valence state of vanadium ions is stable and investigated samples are not degraded during a long time. To clarify the question, the additional ESR measurements were performed for Li₃V₂(PO₄)₃ samples which were air-stored over a long period (up to 2 years). The obtained data proved the sample degradation in the form of increasing in V⁴⁺ content. It was found that in the presence of LiPO₃ salt in the composite the number of magnetic centers increased significantly, so it contributed to sample degradation, while the pure Li₃V₂(PO₄)₃ sample Li₃V₂(PO₄)₃/C were most stable.

The authors investigate the mechanism behind the formation of luminescence centers inside LiF crystals in the short-wave range (400–500 nm). The studied centers are found to be intrinsic crystal lattice defects, created by a radiation–thermal process. The proposed center model is obtained in the NaF lattice. It is established that new centers in sodium fluoride allow short-wave luminescence to be obtained in the yellow-green range.

Results are presented from analyzing the structural and luminescent properties of Ce, Gd co-doped aluminoborosilicate glasses. It is shown that the intensity of luminescence inherent in oxygen-deficiency centers grows along with simultaneously occurring Ce, Gd ions and a nonlinear change in their concentration. This phenomenon correlates with the nonlinear change in glass polymerization and the number of highly symmetrical positions of Gd³⁺ ions. The co-doping effect can be explained by the coexistence of different structural positions of co-dopant ions in a alumino-borosilicate glass matrix and their interaction with intrinsic defects observed in it.

The resonant microwave pulses have been shown to be able to create magnetization of high-spin (S ≥ 1) metal ions even in the absence of an external magnetic field. This transformation of the ion spin states is similar to the “alignment–orientation” transition in atomic spectroscopy. These manipulations make it possible to translate the results of elementary quantum computing operations performed in zero magnetic fields into physically observable quantities.