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

We described the synthesis method and presents the results of a study of the magnetic and magnetotransport properties of vertical hybrid structures Fe₃Si/Ge/Mn₅Ge₃/Si. The mechanisms responsible for the detected magnetoresistive effect and the possible contribution of the spin-valve effect, realized through spin injection/extraction into/from germanium, are discussed.

Quasi-static hysteresis loops of spherical and spheroidal magnetite nanoparticles with semi-axes ratio a/b = 1.5 and 2.0 with different types of combined magnetic anisotropy are calculated using numerical simulation. For particles of each type the critical diameters D_cr are determined so that above D_cr the magnetization curling becomes the easiest mode of particle magnetization reversal. The hysteresis loops are calculated both for single-domain nanoparticles in the diameter range D_cr < D ≤ D_c, and for vortex particles with diameters D > D_c, where D_c is the single-domain diameter. The results obtained are compared with the hysteresis loops of single-domain particles with uniform magnetization rotation. The remanent magnetization and coercive force of oriented and non-oriented dilute assemblies of magnetite nanoparticles with different aspect ratios are determined as the functions of the transverse particle diameter.

We consider the spin wave resonances (SWRs) magnetoelastic excitation and electric detection in a hybrid bulk acoustic wave resonator containing YIG/Pt bilayer. The influence of micrometer and submicrometer yttrium iron garnet (YIG) film thickness on the efficiency of SWR excitation accompanied by a spin pumping from YIG to Pt has been theoretically studied. The frequency and thickness dependencies of inverse spin Hall effect (ISHE) voltage and microwave reflection coefficient are analytically and numerically investigated and discussed. Due to the non-uniform effective magnetic field of elastic nature, the higher SWR modes (both even and odd) can be excited with an efficiency comparable to the efficiency of the fundamental mode at the ferromagnetic resonance frequency. If an integer number of acoustic half-waves fits into the YIG film thickness, forbidden zones arise in the SWR spectrum: at certain thickness values, only even or only odd SWR modes are excited.

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.

We presented the research results by impedance spectroscopy of frequency-dependent temperature activation of the conductivity and dielectric constant of the single-crystal magnetoelectric bismuth ferrite BiFeO₃, a promising functional material for RAM devices. The activation energies of low-temperature (110–300 K) processes of motion of charge carriers of the multiferroic structure and the logarithmic dependence of the critical temperatures between these processes on the frequency are determined in AC regime. It has been established that in this temperature range there is a correlation of AC characteristics with low- to high-temperature activation of the parameters of the BiFeO₃ crystal lattice.

We presented a setup created on the RADEX neutron channel at the Institute for Nuclear Research of the Russian Academy of Sciences to study the properties of highly excited states of light nuclei. The first experiment was carried out on the setup to determine the cluster structure of highly excited states of the ⁶Li nucleus in the reaction ⁶Li(n, ³He n)³H at a neutron energy of 50 ± 5 MeV. Several variants of the data collection system have been tested. A preliminary spectrum of the excitation energies of the ⁶Li nucleus has been obtained.

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.