Том 44, № 7 (2018)

Relaxation losses of magnetic excitations in nanoscale films of Y₃Fe₅O₁₂ (YIG) were studied. The films were obtained by laser molecular-beam epitaxy (LMBE). Ferromagnetic resonance linewidth ΔH was found to increase sharply as the temperature decreased from 300 to 77 K. The observed growth of ΔH is explained by typical relaxation processes caused by the presence of Fe²⁺ ions. This effect is not observed in thick films of YIG grown by liquid-phase epitaxy and containing Pb⁴⁺ ions, and, hence, we have concluded that the presence of acceptor ions in YIG films obtained by LMBE will facilitate decreasing the concentration of Fe²⁺ ions and, a result, diminishing relaxation losses.

A Fourier component of the potential energy of interaction between two atoms has been presented as a polynomial of the biquadratic atomic form factor. A numerical calculation has been performed in the screened Coulomb potential approximation. It is demonstrated that the account for the Pauli principle leads to the occurrence of a potential barrier and an additional region of attraction of two atoms. This model is shown to agree qualitatively with the results of the density-functional-theory calculation.

Secondary-ion mass spectrometry and Rutherford proton backscattering have been used to measure the concentration profiles of nitrogen atoms and examine the defect structure of epitaxial GaAs layers implanted with 250-keV N⁺ ions at doses of 5 × 10¹⁴–5 × 10¹⁶ cm^–2. It was found that no amorphization of the layers being implanted occurs at doses exceeding the calculated amorphization threshold, a concentration of point defects that is formed is substantially lower than the calculated value, and a characteristic specific feature of the defect concentration profiles is the high defect concentration in the surface layer.

A high-quality superconducting resonator with a microbridge of hafnium film for use in a circuit for readout a terahertz-band imaging array with frequency division multiplexing is demonstrated experimentally. The variability of the impedance of the bridge at a frequency of 1.5 GHz, which is a key factor in the control of the quality of the resonator, is studied. The bridge, having a thickness of about 50 nm, a critical temperature T_C ≈ 380 mK, and a plan size of 2.5 × 2.5 μm, was connected as a load of a resonator made of niobium film with a thickness of about 100 nm (T_C ~ 9 K). It is shown that the bridge smoothly changes its impedance proportionally to the bias power in the entire temperature range. The effective thermal insulation of the bridge was measured in a dilution cryostat at temperatures of 50–300 mK. Thermal conductivity G of the bridge was calculated and found to be ~4 × 10^–13 W/K, which gives an estimate of the sensitivity of the structure in the bolometric mode NEP ≈ 8 × 10^–19 W/Hz^1/2 at a temperature of 150 mK.

The correlation between lattice characteristics of a deformed medium and parameters of autowaves of a localized plastic flow in metals at the stage of linear strain hardening is considered. Such correlation testifies for the existence of a close connection between elastic and plastic deformations of the medium and, more generally, between characteristics of plasticity and electronic structure of elements.

Ultrathin polycrystalline Fe films have been grown on the oxidized surface of a Si(001) substrate. The resistivity and magnetic hysteresis of Fe films have been measured in the range of thickness from 2.5 to 10 nm. Based on the analysis of the data obtained, it is suggested that there is a transition to the structurally continuous film at a thickness of ~6 nm. It is found that Fe grains in this film acquire the preferred (111) orientation during this transition.

A design of a magnetic shutter for a trap made of permanent magnets for the ultracold neutron storage in experiments on measuring the neutron lifetime is proposed. The data of shutter testing and comparison with the calculated magnetic fields are reported.

Experimental data on the influence of neutron irradiation on the plasticity characteristics of chromium–nickel austenite steels have been analyzed. Special attention is devoted to detection of anomalously high plasticity levels attained at some parameters of irradiation and deformation, which is explained by the formation and propagation of a “phase transformation wave” in the metastable steel. Necessary and sufficient conditions for the realization of this wave are formulated.

We describe a method of obtaining ultrafine boron carbide (B₁₃C₂) powder using the effect of a dc electric arc on a mixture of initial reactants containing carbon and boron. A peculiarity of the proposed method is that it can be implemented using arc discharge operating in open air without any vacuum equipment and protective inert gas atmosphere. X-ray diffraction data showed that the synthesized product in the general case contained three crystalline phases: boron carbide (B₁₃C₂), graphite (C), and boron oxide (B₂O₃). Electron-microscopic examination showed that the average size of boron carbide particles ranged from ~50 nm to ~2 μm.

The upconversion luminescence (UCL) of nanocrystalline gadolinium oxide (Gd₂O₃) doped with Er³⁺ and Yb³⁺ ions has been studied in the temperature range of 90–400 K. The nanocrystals were synthesized by chemical vapor deposition and possessed a cubic crystalline structure with an average particle size within 48–57 nm. It is established that the USL intensity in the red (⁴F_9/2 → ⁴I_15/2 transition in Er3+ ion) and green (⁴S_3/2 → ⁴I_15/2 transition) spectral regions depends on the sample temperature and concentration of dopant ions, as well as on the additional structural defects (anion vacancies) created in the crystal lattice by the introduction of Zn²⁺ ions or irradiation with high-energy (10 MeV) electrons. The luminescence efficiency and spectrum of the upconversion phosphor are determined by energy transfer processes.

Silicon surface morphology induced by a femtosecond laser pulse at near-threshold fluences in water environment is investigated by means of atomic-force microscopy (AFM). With increasing fluence, the silicon surface transforms into nanoscale ring-shaped and blister structures, as well as smooth and nanostructured microcraters with a minimum depth of 1 nm. The formation of starlike patterns imprinted at the surface of microcraters at fluences above the ablation threshold is observed.

The formation of titanium nanoparticles (NPs) in a high-voltage electric discharge between titanium electrodes in liquid xenon at a temperature of –105°C has been observed. It has been shown that these titanium nanoparticles have a spherical shape with an average diameter of <50 nm and they possess high chemical activity. This makes it possible when a relative mass concentration of NP reaches ~10^–6 to efficiently purify xenon from electronegative impurities for its use as a working medium for a new generation of high-efficiency nuclear radiation detectors.

Giant macroscopic expansion of the surface relief, localized within a laser spot size, has been observed in bulk single crystals of TlInSe₂, TlGaTe₂, and TlSe at room temperature and laser radiation densities lower by at least two orders of magnitude than the material optical damage threshold. Quantitative estimations of the deformation magnitude in this local region were obtained using an interference dilatometer. The photon absorption length was determined with the aid of spectroscopic ellipsometry. It is established that the surface deformation amounts to 2.6 × 10^–3 at a laser radiation intensity of 19 mW/mm². The observed phenomenon has a thermal nature and is probably related to a low thermal conductivity of the materials studied.

We have studied the structure and properties of porous nickel titanium (TiNi) alloys obtained upon reaction sintering of Ti and Ni powders with Co and Mo additives. It is established that Co and Mo doping additives retain the compaction of Ni powder achieved at the initial stage of sintering. The maximum deformation of porous samples loaded in the austenite state was observed upon adding Co, while the addition of Mo resulted in minimum deformation. The addition of Co leads to single-stage martensitic transformation in TiNi phase, while the addition of Mo leads to the two-stage transformation that is more homogeneous over the volume. Both Co and Mo additives lead to increase in the maximum accumulated strain due to the formation of favorably oriented stress-induced martensite and reoriented quench-induced martensite.