Anomalies of the magnetic and magnetoelastic properties of rare-earth (RE) tetragonal paramagnetic materials with zircon and scheelite structures resulting from the interaction of the energy levels (crossover) of an RE ion in a strong magnetic field up to 400 kOe are discussed. Using the example of HoPO$_4$, the specific features of magnetic properties are compared for a crossover with and without a gap in the magnetic field along the [100] and [110] axes. Anomalies of linear magnetostriction at a crossover in a strong magnetic field with DyPO$_4$ are discussed. Calculations within the formalism of the crystal field are shown to give an adequate description of magnetic and magnetoelastic anomalies and critical parameters of the crossover of the investigated crystals when using known interaction parameters, under the assumption of an adiabatic magnetization process in pulsed fields. Taking HoVO$_4$ as example, the anomalous magnetocaloric effect near the crossover is discussed when a crystal is cooled to temperatures of approximately 0.1 K as the field increases, with the starting temperature being $T_{\rm st}=4.2$ K. The step-like change of the contribution of the quadrupole interactions in a number of the crystals caused by the change of the quadrupole moments at the crossover is noted as an analogue of the induced quadrupole transition.
Show AbstractThe phenomenon of temperature-induced itinerant electron metamagnetism in a zero external field is of the same nature as the widely investigated metamagnetic transitions induced by magnetic fields (external or internal). Recently, temperature-induced itinerant metamagnetism was discovered in the rareearth intermetallic RCo$_3$ compounds. Systematic investigations of the RCo$_3$ series made it possible to determine many specific features of this new phenomenon and to formulate criteria to reveal such transitions in other magnetic materials as well. This paper presents a brief review of the existing works and original results on temperature-induced itinerant-electron metamagnetism in substituted RCo$_3$ compounds.
Show AbstractThis article discusses experimental data and their theoretical interpretation concerning the volume magnetostriction, spontaneous magnetostriction, variation of magnetization under the action of pressure, and elastocaloric effects in rare-earth metals, as well as their alloys and compounds. Particular attention is paid to the region of phase transitions. The volume magnetostriction $\omega$ of true magnetization was investigated near the Curie temperature $\Theta$ as a function of magnetization and determined from the change of magnetostriction under the action of pressure. From these data we obtained the dependence of the exchange integrals on the unit cell volume. Giant volume magnetostriction and magnetoelastic elastocaloric effects were discovered in the rare-earth metals and alloys in the region of their magnetic phase transitions. It was established that giant volume magnetostriction in RCo$_2$ compounds is caused by a critical increase of the magnetic moment of the $3d$ sublattice of cobalt in magnetic fields that exceeds the critical field at ${T>\Theta}$. Giant volume magnetostriction in R$_2$Fe$_{17}$ compounds near the temperature $\Theta$ is shown to occur due to strong deformational dependences of exchange interaction and the value of the $3d$ electron bandwidth.
Show AbstractA study of thermal expansion and magnetostriction caused by the metamagnet phase transition in a rare earth sublattice was performed for a DyAlO$_3$ single crystal, which is the model object of a wide family of rare earth oxides with the structure of distorted perovskite. The sharp variation of the relative strains along the $b$ axis ${3.6\cdot10^{-5}}$ was found at ${T\cong2.18}$ K. The nature of the observed anomaly is caused by the occurrence of a metastable state of the magnetic subsystem achieved in the conditions of the experimental process. The relaxation of magnetostriction is studied and the exponential character is found. The possible mesoscopic nature of thermal and quantum mechanisms of magnetic relaxation is considered.
Show AbstractDielectric dispersion is studied in films made of vinylidene fluoride/trifluoroethylene copolymer [P(VDF/TrFE)], which are obtained by the Langmuir-Blodgett technique in the temperature range from ${-}$90 to ${+}$132$^0$C. The thickness of the films studied is ${\sim}$7 nm. A glass transition is observed in the temperature range from −40 to −50°C; this indicates the presence of an amorphous phase in the ultrathin Langmuir-Blodgett films.
Show AbstractPreviously formulated physical principles are used to develop a mathematical model of thermally induced processes of diffusion, phase formation, and stabilization of a spatially inhomogeneous structural-phase state in layered systems containing three isotopes of two elements. The program realization of the model allows quantitative characterization of the kinetics of these processes under arbitrary conditions of thermal annealing. The results of theoretical calculations and the experimental data obtained by Mössbauer spectroscopy and X-ray diffractometry of the layered structure consisting of $^{57}$Fe(0.07 μm)-Ti(1 μm)-Fe$_{0.96}$Ti$_{0.04}$(13 μm)-$^{57}$Fe(0.07 μm) are found to be in good agreement.
Show AbstractThe band structure, size quatized levels, and wave functions in the conduction and valence bands of strained n-Al$_{x}$Ga$_{1-x}$As/GaAs$_{y}$P$_{1-y}$/p-Al$_{x}$Ga$_{1-x}$As (y = 0.84) heterostructures are calculated numerically upon a uniaxial compression along the [110] direction. The calculation indicates a sublinear increase of the effective optical gap in the GaAs$_{0.84}$P$_{0.16}$ quantum well, strong mixing of states of light and heavy holes, and merging of the corresponding ground states in the quantum well of the valence band under a pressure of 4.5–5 kbar. The calculation of matrix elements of the electron-photon interaction operator for a system of possible interband transitions permits one to determine the optical gain for the TE and TM modes. The increase in this coefficient by two to fourfold under uniaxial compression agrees with the previously published experimental data on the increase of the electroluminescence intensity.
Show AbstractA highly effective adsorbent based on linear-chain carbon is studied by infrared spectroscopy, Raman spectroscopy, X-ray microanalysis, and X-ray diffraction analysis. The structure and the properties of amorphous linear-chain carbon are investigated.
Show AbstractThis article presents a method for the construction of a dependency graph for the 24 Delaunay types in terms of increasing symmetry. This method allows one to find symmetrical-topological dependencies between all 24 types.
Show AbstractThe model of variable range hopping is generalized to systems with extended sites. The calculation of the hopping conductivity of a disordered medium with chain structure is reduced to the percolation problem for a system of one-dimensional fragments with random distribution of lengths and orientations. The percolation problem is solved using the Monte Carlo method and the method based on the bonding criterion. The percolation threshold, which determines the dependence of the conductivity on the fragment lengths and degree of their orientational ordering (texture), is calculated. It is shown that the conductivity increases exponentially with fragment lengths and decreases with orientational ordering.
Show AbstractA new method for obtaining the well-known Karnahan-Starling equation for systems of hard spheres and its generalization for the case of any number of precisely known virial coefficients is proposed. The efficiency of the method for the construction of the statistical thermodynamics of a system of soft spheres, where an analytical expression for free energy and equations of state that agree well with the data of the computer experiment are found, is shown. The considered approach is generalized for systems with a positive definite potential of interaction between particles.
Show AbstractThe application of the mixed finite-element method for the analysis of dispersion curves of the cylindrical waveguides with a gradient loading is considered. The test results of the algorithm and the calculations of systems with a variable refractive index are presented. The initiation of complex waves in layered waveguides is shown.
Show AbstractThe modification of the Discrete Sources Method, which allows one to perform effective numerical analysis of plasmon resonances in local structures, is proposed and realized. The numerical algorithm allows computation of the near field with a high degree of accuracy and tracking resonances that cause an increase of the near-field intensity by several orders of magnitude.
Show AbstractA method for estimating the parameters of turbulence that was originally developed for collimated laser beams is applied to the case of a divergent beam. The estimate is based on an analysis of the correlation functions of the Zernike expansion coefficients of the phase. The results suggest that the method can be used for the estimation of the inner scale of turbulence in an experiment with a divergent laser beam. In the case of isotropic turbulence, it is also possible to estimate the outer scale of turbulence from the correlation functions of lower-order modes.
Show AbstractCosmic strings are theoretically predicted linear structures of a cosmological size. The search for cosmic strings in optical and radio observations has been an important area of research in recent years. One of the most effective methods of searching for these objects is the analysis of the anisotropy of cosmic microwave background radiation that could be induced by cosmic strings. For this purpose, the authors propose a method of signal expansion in modified Haar functions with cyclic translations. However, for a system of these functions to be used correctly, one needs to prove its orthonormality and completeness, which is the purpose of this paper.
Show AbstractThis paper analyzes the hypothetical influence of variability in the velocity of light associated with the motion parameters of a source on the results of spectral measurements of stars within an exoplanet search program. The accelerations of stars relative to the barycenter of the host star-planets system are taken into account. The dependence of the velocity of light on the barycentric radial velocity and the radial acceleration components of the barycentric stars is shown to lead to a substantial increase (up to an order of magnitude) in the semimajor axes of the orbits of detected candidate extrasolar planets. Consequently, a correct comparison of the spectral method with other well-known modern methods for detecting extrasolar planets allows one to consider the results obtained in this paper as a reliable test for the invariance of the velocity of light.
Show AbstractResearch was carried out to estimate the possibility of determining the direction and strength of the ancient geomagnetic field $(\textbf{H}_{\rm an})$ by natural remanent magnetization ($\textbf{I}_n$) of nine oriented samples from traps of the Minor Botuoba Region (Yakutia) aged 260 Ma. Five samples (Pi-10, K-4, K-6, 315–13, and Ki-2) are characterized by negative polarity of $\textbf{I}_n$, while four samples (nos. 334-5, 331–2, 315–11, 299–2) have positive polarity as does the recent geomagnetic field in this region. The ferrimagnetic constituent of the samples with reverse I n polarity appears to be quite variable: samples K-4 and K-5 are characterized by low Curie points ($T_c\approx200^{\circ}$C) of the ferrimagnetic phase, sample Ki-2 contains single-phase oxidized titanomagnetite with $T_c\approx310^{\circ}$C, and the $T_c$ of the Pi-10 ferrimagnetic phase is 540°C. Hence, it may be concluded that the primary remanent magnetization of the first two samples was formed in a reverse polarity field. These samples also may be used to determine the paleostrength of the geomagnetic field. The properties of traps containing single-phase oxidized (sample Ki-2) and disintegrated (sample Pi-10) titanomagnetite require additional investigation. Samples with positive $\textbf{I}_n$ polarities are characterized by the self-reversal phenomenon upon thermal demagnetization of the natural remanent magnetization, which was most likely caused by the occurrence of titanomagnetite exsolution textures in ferrimagnetic grains. The paleoinformation value of the $\textbf{I}_n$ of these samples is doubtful.
Show AbstractDetailed analysis is presented of the well-known Tatarskii’s formula, which describes sound wave scattering in a turbulent atmosphere. The adiabaticity of the acoustic fluctuations and incompressibility of the turbulent fluctuations are assumed only. This yields to additional 1 terms in the classical formula (probably, small in the inertial range of turbulence). We show the change of Obukhov’s formula, which describes the connection between turbulent fluctuations of pressure and velocities in a compressible atmosphere, and also demonstrate the effect of the independence of fluctuations of the potential and thermodynamic temperatures. By analogy with the formula for small-scale isotropic temperature fluctuations, which was also obtained by Obukhov, we derive a formula for the fluctuations of entropy and potential density as function of entropy, which describes spatial distribution of the probability density of identical “fluid particles” in the turbulent media.
Show AbstractThe dynamics of the Earth’s outer radiation belt were traced at altitudes of 500–830 km during weak geomagnetic disturbances based on the data of simultaneous experiments carried out in November 2009 onboard the CORONAS-Photon solar observatory and the Meteor-M No. 1 artificial satellite. The average statistical profile of external boundary of the outer radiation belt that is characteristic for a quiet magnetosphere has been found from the analysis of variations in the position of the polar boundary of the capture region in the Earth’s magnetosphere.
Show AbstractA mathematical model of a waveguide with re-entrant corners in its variable cross section is considered. The influence of the re-entrant corner on the waveguide field mode structure is investigated.
Show AbstractA new approach to investigate diffuse matter in space is proposed. It is based on registration of high energy neutrons. The high energy (hundreds of GeV) neutrons decay length is comparable to distance to the Cuiper belt. The neutrons decay destructs the interstellar background. It is shown that the expected high energy neutrons flux can be registered by the perspective devices (we used data on gas and dust density obtained by an analysis of space apparata trajectories).
Show AbstractDynamic parameters of movement of the Sun concerning the center of mass of Solar system – distance of the center of the Sun concerning the center of mass, the angular moment of the Sun and its change are investigated. Frequency spectra of these parameters and Volf's numbers are calculated, the basic spectral components are revealed. It is shown that periodicity of 178.8 years is not predominating in mechanical parameters of movement of the Sun, and in this range of frequencies the periodicity of 169 years connected with influence of the Neptune predominates. Coincidence of periodicity in Volf's numbers and dynamic parameters of movement of the Sun is shown. The reasons of all components of a frequency spectrum are specified.
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