Influence of the special features of the effective magnetic anisotropy on the temperature dependences of the magnetoimpedance of nanocrystalline Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> strips

The influence of the thermal treatment type on the temperature dependences of the magnetoimpedance of nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy strips is investigated. The main mechanisms determining the temperature behavior of the magnetoimpedance of strips with induced magnetic anisotropy having various special features are established. The prospects for application of the alloy strips nanocrystallized in the presence of a magnetic field as sensitive elements of temperature sensors and special magnetic field detectors are demonstrated.     

Investigation of low-lying levels of the <Stack><Subscript>4</Subscript><Superscript>8</Superscript></Stack>Be nucleus in the multiquantum approximation of the orthogonal scheme

In the multiquantum approximation of the orthogonal scheme, specific calculations for the energies and radii of the ₄ ⁸ Be nucleus are performed with allowance for all states characterized by the λ=[44] Young diagram, the quantum numbers K_min and K_min+2 of the O(3(A?1)) group, and the quantum numbers E=K+2N (N≤9) of the U(3(A?1)) group. The convergence of the results with respect to the extension of the basis is studied, and the structure of relevant wave functions is revealed. The results of these calculations are compared with the results obtained in the analogous approximation of the unitary scheme.     

Magneto-optical investigations of the domain structure and magnetization of the ferrite-garnet Tb<Subscript>0.2</Subscript>Y<Subscript>2.8</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> in the temperature range of the spontaneous spin-reorientation phase transition

The transformation of a domain structure and technical magnetization of the Tb_0.2Y_2.8Fe₅O₁₂ single crystal in the temperature range of the spontaneous orientational phase transition have been investigated by the magneto-optical method. It has been shown that the phase transition is extended in a certain temperature range in which domains of the low-temperature and high-temperature magnetic phases coexist. It has been found that the evolution of the domain configuration in the temperature range of spin reorientation substantially depends on the presence of mechanical stresses in the crystal. Anomalies in the temperature dependences of the coercivity and magneto-optical susceptibility of the crystal due to the transformation of its domain structure during the phase transition have been revealed. The experimental results have been interpreted within the existing theory of orientational phase transitions in cubic crystals.     

Energy spectrum of the low-lying states in Sr<Subscript>2</Subscript>FeSi<Subscript>2</Subscript>O<Subscript>7</Subscript> and the nature of the magnetoelectric effect

A mechanism underlying the magnetoelectric effect is discussed. This mechanism is related to the combined action of an odd crystal field, spin?orbit coupling, and the interaction of the orbital angular momentum with an applied magnetic field. The effective operator describing the spin states of Fe²⁺ ions is obtained. Such operator allows one to interpret the terahertz spectroscopy data and to calculate both the electric field effect on the magnetization and the magnetic field effect on the electric polarization of the sample. It is demonstrated that the magnetoelectric effect is enhanced with a decrease in the energy corresponding to the tetragonal distortion of ligand tetrahedra.     

Effect of the atomic composition of the surface on the electron surface states in topological insulators A<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>B<Stack><Subscript>3</Subscript><Superscript>VI</Superscript></Stack>

The results of the theoretical investigation of the surface electronic structure of A₂^VB₃^VI compounds containing topologically protected surface states are reported. The ideal Bi₂Te₃, Bi₂Se₃, and Sb₂Te₃ surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces, have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces formed by semimetal atoms. The fraction of such terraces on the surface has been estimated.     

On the nature of the KH<Subscript>2</Subscript>PO<Subscript>4</Subscript> high-temperature transformation

For over two decades, the high-temperature phase transition (HTPT) at around T _p = 180 °C on KH₂PO₄ (KDP), which involves an ionic conductivity increase, constitutes a controversial subject; while most authors ratify a physical transformation (tetragonal → monoclinic phase transition), others defend the chemical transformation. A careful high-temperature phase behavior examination of this acid salt by means of modulated and conventional differential scanning calorimetry, thermogravimetric analysis, simultaneous thermogravimetric and differential scanning calorimetry, impedance spectroscopy, and temperature evolution of X-ray diffraction was performed to provide a possible solution to this long-standing issue. We found that the structural phase transition does not take place. Instead, a chemical transformation occurs at T _p. When KDP is heated through this temperature, the sample initially corresponding to a single phase (tetragonal) transforms to a sample composed of two solid phases: tetragonal KDP, located at its bulk, and monoclinic potassium metaphosphate (KPO₃), located at its surface. Most of the water produced evaporates, but a small portion of liquid water bonds to KPO₃. Because this is of polymeric nature, it takes the role of a host matrix that contains liquid water regions. Consequently, given that part of the water dissolves a portion of surface salt (providing protons), the surface sample system behaves in a similar manner to a polymer electrolyte membrane where the proton transport mechanism includes the vehicle type, using hydronium (H₃O⁺) as a charge carrier. On further heating, the bulk tetragonal KDP phase reduced to its total decomposition. The metastability of the high-temperature phase below T _p is also explained.     

On the interpretation of the phase diagram of La<Subscript>2−x</Subscript>M<Subscript>x</Subscript>CuO<Subscript>4</Subscript>

The difference between the phase diagrams of La_2?x(Ba,Sr)_xCuO₄ and Nd_2?xCe_xCuO₄ is discussed. It is proposed that the discrepancy of x-values corresponding to the transition from antiferromagnetic dielectric state to conducting one (respectively, x≈0.06 in La_2?x(Ba,Sr)_xCuO₄ and x≈0.125 in Nd_2?xCe_xCuO₄) results from non-homogeneous doping of La_2?x(Ba,Sr)_xCuO₄ over the range 0.06<x<0.125, when localized holes are added to each second CuO₂ layer. Therefore the actual phase diagram of the “holedoped” superconductor La_2?x(Ba,Sr)_xCuO₄ coincides with one for the “electron-doped” superconductor Nd_2?xCe_xCuO₄. It is shown that all features observed in La_2?x(Ba,Sr)_xCuO₄ around x=0.125 are clarified on this basis.     

Study of the formation and stability of the NdSr<Subscript>2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>7</Subscript> phase

The sequence of phase equilibria during synthesis of the NdSr₂Mn₂O₇ phase is determined. The stability of this phase with changes in temperature and partial oxygen pressure is investigated.     

Critical behavior of the heat capacity of the manganite La<Subscript>0.87</Subscript>K<Subscript>0.13</Subscript>MnO<Subscript>3</Subscript>

The heat capacity of the manganite La_0.87K_0.13MnO₃ has been measured in the temperature range 80–350 K. The nature of the ferromagnetic phase transition and the critical properties of heat capacity near the Curie temperature have been studied. The regularities of variations in the universal critical parameters near the phase transition point have been established. The calculated critical exponent and amplitudes of the heat capacity with allowance for corrections on the scaling (α = −0.13 and A ⁺/A ⁻ = 1.178) correspond to the critical behavior of the 3D Heizenberg model.     

On the two-loop corrections to the pole mass of the <Emphasis Type="Italic">B</Emphasis> quark in the gaugeless limit of the MSSM

We present the result for the two-loop corrections to the pole mass of the b quark in the gaugeless limit of the MSSM. In this limit, we assume that the contribution from the electroweak gauge interactions is small, so we can set all the corresponding couplings in the Lagrangian of the MSSM to zero. The result presented here differs from one obtained earlier, especially in some particular regions of the MSSM parameter space. The text was submitted by the authors in English.     

Proof of the Cases <Emphasis Type="Italic">p</Emphasis>≤ 7 of the Lieb-Seiringer Formulation of the Bessis-Moussa-Villani Conjecture

It is shown that the polynomial λ (t)=Tr[(A+ tB)^p] has nonnegative coefficients when p≤ 7 and A and B are any two complex positive semidefinite n× n matrices with arbitrary n. This proves a general nontrivial case of the Lieb-Seiringer formulation of the Bessis-Moussa-Villani conjecture which is a long standing problem in theoretical physics.