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

We used a 55 nm [Ru(dipy)₃]²⁺@SiO₂ nanophosphore as a temperature sensor under photobleaching conditions. We have calibrated these nanoparticles for temperature measurements using/analyzing both luminescence intensity and decay time change. We show that an exposure to a 405 nm semiconductor laser with a power flux density of 2 kW/cm² leads to a two-fold decrease in luminescence intensity over time. At the same time (4 h), the characteristic decay time of the luminescence decreases by approximately half. We demonstrate that a ratiometric method is more reliable for temperature measurements in the range from 300 to 350 K. This method takes approximately half the time required to measure the kinetics of luminescence decay.

To study detonation and shock wave processes as part of experimental stations at the SKIF Center for Shared Use, it is planned to build a “Fast Processes” station. The station will include DIMEX detectors (Detector for imaging of explosions). DIMEX is capable of detecting synchrotron radiation (SR) from each electron bunch in the storage ring. Since bunches can deviate from the equilibrium orbit and differ in current, to increase the accuracy of signal magnitude measurements, a fast monitor of the position and intensity of the SR beam is needed, measuring the relative position and power of the beam radiation from each electron bunch in the storage ring. The readings from this monitor will be used to correct the measurements of the DIMEX detectors. As part of the fast SR beam position monitor, it is planned to place 4 sensors that measure the signal in the vicinity of the beam at the top, bottom, right and left. When the beam position changes, the signal ratios in the corresponding pairs of sensors will change. When the total SR flow changes, the sum of the signals from all sensors will change. The beam monitor, synchronously with the operation of the DIMEX detector, will record signals from all sensors during the experiment. After the experiment, the results recorded from the DIMEX detector will be adjusted in accordance with the monitor sensor signals.

We studied the morphological, structural, and optical studies of hydrophobic up-conversion NaYF₄:Yb/Ho nanoparticles synthesized by the thermal decomposition method. To impart hydrophilic properties, the NaYF₄:Yb/Ho nanoparticles were silanized using the following nonionic surfactants: Triton X-114, Tween 85, and PEG monooleate. As a result, a silicate shell formed on the surface of the nanoparticles, providing hydrophilic properties and stable colloidal solutions in water while maintaining their luminescent characteristics. The use of the most effective surfactant, Triton X-114, for silanization allowed for obtaining a narrow size distribution of NaYF₄:Yb/Ho@SiO₂ nanoparticles. The study of the temperature dependencies of luminescence spectra indicates the high potential of NaYF₄:Yb/Ho and NaYF₄:Yb/Ho@SiO₂ nanoparticles for use as luminescent temperature probes.

Using the example of two-layer tantalum-permalloy films, we studied the possible effects of enhancing the magneto-optical response and changing the magneto-optical spectrum in multilayer magnetic structures. The sputtering of a thin paramagnetic or diamagnetic film on permalloy can change the optical and magneto-optical parameters of permalloy due to the redistribution of atoms near the interface between the layers, or due to mechanical deformations. On the other hand, due to the effect of magnetic proximity, spin polarization may occur in a non-magnetic layer. The results of computer simulation of the transverse Kerr effect for a single-layer permalloy film with variations in its optical and magneto-optical parameters and a two-layer tantalum-permalloy system are presented, as well as a comparison of the calculation results with experiment.

The conditions for the formation of clusters (lattices and chains) of spiral magnetic domains in the thin magnetic film with perpendicular magnetic anisotropy have been established by the numerical simulation method within the Ginzburg–Landau approach. The results of the numerical simulation are compared with the experimentally established regularities of the formation of the spiral domain chains and lattices in iron garnet films.

We studied the evolution of the phase composition of laser welded joints before and after heat treatment of 3rd generation Al–Li alloys using synchrotron radiation. The article demonstrates the fundamental role of the alloying elements of copper and lithium in formation of the phase composition of the fusion zone of the weld. It has been established that laser exposure changes the phase composition of the alloy. Namely, low copper contents mainly lead to formation of T₂(Al₆CuLi₃) and T₃(Al₅CuLi₃) phases, the average copper contents form T₁(Al₂CuLi), T₂(Al₆CuLi₃), T₃(Al₅CuLi₃) phases and the presence of high copper contents results in formation of T₁(Al₂CuLi) phase at the boundaries of dendrite. Post-heat treatment restores the initial phase composition in the fusion zone. As for the solid solution, the δ'(Al₃Li) phase is formed at low copper contents, the δ'(Al₃Li) and T₁(Al₂CuLi) phases are formed at average copper contents, and T₁(Al₂CuLi) phase is observed at high copper contents. Consequently, this makes it possible to improve the mechanical properties of weld joint specimens to match the numbers of the initial alloy.

We considered a domain wall as a structure which shifts the phase of a propagating spin wave under the condition of applied electric field by means of an inhomogeneous magnetoelectric coupling. The result is that the electrically induced transition of the Bloch domain wall into the Néel domain wall changes the phase of spin wave passed through the domain wall by nearly 180°.

X-ray diffraction on synchrotron radiation was used to analyze kidney stones as part of phantom objects simulating the patient’s body. The radiation photon energies were 33.7, 67 and 112 keV. It has been shown that the use of synchrotron monochromatic radiation with photon energy E ≥ 67 keV allows one to reliably identify the mineral composition of uroliths. The shift to a higher photon energy range can significantly reduce the radiation load on patients during diagnosis. The patient’s weight factor also becomes less critical.

The structure, magnetic properties and ferromagnetic resonance curves of cobalt ferrite particles synthesized by chemical coprecipitation technique have been studied. The possibility of resonant heating of powder in a magnetic anisotropy field of particles is shown, which can find application in medicine for magnetic hyperthermia.

Concentration and angular dependences of the parameters (line width and position) of ferromagnetic resonance (FMR) for CoTaNb/MgO composite films with metal alloy concentrations x = 0.27–0.72 were obtained in the work. Granular, granular-percolation structure and zigzag stripe magnetic structure for films with different x were detected. An increase in the FMR parameters with an increase in the angle from 0° to 90° between the constant magnetic field and the film plane with different x was observed. It was shown in the work that the behavior of the angular dependences strongly depends on the magnetic structure of the films, which have the greatest change in the region of transition from granular to granular-percolation structure with extended magnetic metallic microregions. The FMR method is a structure-sensitive method for scientific studies of the electromagnetic properties of thin magnetic composite films with granular and percolation structures and their combinations was demonstrated.