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

The evolution and relaxation of MQ NMR coherences on the preparation period were investigated experimentally on a single crystal of gypsum, CaSO₄·2H₂O. The theory describing the dynamics of MQ coherences on the preparation period of MQ experiment for a pair of spins was developed based on the Lindblad master equation. This theory predicts the appearance of MQ coherences of only zeroth and second orders, oscillatory exchange of their intensities and exponential decay with increasing of the preparation time. The proposed theory describes the experimental data well. It is shown that the frequency of oscillations depends on the orientation of the crystal in the external magnetic field and determined by the dipolar coupling between protons of the water molecules contained in the gypsum crystal. The relaxation time of MQ coherences of zeroth and second orders, T_r = 150 ± 15 μs, were independent of the crystal orientation, which suggest a common source of relaxation due to the dipole-dipole interactions with protons surrounding water molecule.

The static magnetic properties were experimentally studied and magnetization reversal was modeled in an epitaxial thin film of the L1₀ phase of the PdFe compound and the PdFe/W/PdFe heterostructure on MgO (001) substrates. It was shown that the PdFe/W/PdFe heteroepitaxial structure at an α-W layer thickness of ∼0.7 nm is an artificial antiferromagnet with perpendicular magnetic anisotropy and an exchange integral of (J simeq 1.7 times {{10}^{{ - 3}}},,{text{J/}}{{{text{m}}}^{2}}). Micromagnetic modeling of the equilibrium domain structure and its evolution in an external magnetic field made it possible to satisfactorily describe the magnetization reversal curve of the studied thin-film heterostructure.

The influence of the configuration of ions (Zn²⁺(3d¹⁰), Co²⁺(3d⁷), Co³⁺(3d⁶), Mg²⁺(2p⁶)) replacing manganese in La–Sr manganites on crystal lattice parameters, magnetization, Curie point, semiconductor-metal transition and magnetoresistance has been established. The composition with cobalt in the state of Co³⁺(3d⁶) has the highest values of magnetic parameters, and Mg-containing manganite has the lowest values, but it exhibits the maximum magnitude of magnetoresistance.

Single color centers in sodium fluoride crystals were studied for the first time. The quantum trajectories of the intensity of three types of luminescence centers emitting in the visible region of the spectrum were observed, one of which is the ({text{F}}_{3}^{ + }) center. The quantum trajectories were determined to be flickering. Their flickering is caused by transitions of the centers from the excited singlet state to the triplet state and, further, to the ground singlet state. The average lifetime of the ground triplet state of ({text{F}}_{3}^{ + }) centers as measured from the quantum trajectories of luminescence of single centers is 1.9 s, which coincides with the results of past measurements of the decay kinetics of triplet luminescence of an ensemble of ({text{F}}_{3}^{ + }) centers.

Spectral and kinetic characteristics of photoluminescence of BaF₂ and SrF₂ crystals implanted with high-energy (∼100 keV) Ag ions were studied. The photoluminescence spectra of both crystals have a similar structure, in which three components are observed with maxima in the wavelength ranges 500–550, 600–670, and 760–770 nm. The positions of the maxima depend on the material of the matrix and the excitation wavelength. The kinetic curves of luminescence decay also exhibit three components with characteristic decay times of ≤1, about 4, and 13–15 ns.

The Ornstein–Zernike integral equations for thermodynamically equilibrium liquids are considered, taking into account irreducible diagrams. An algorithm for calculating the first irreducible diagram is formulated for a spatially homogeneous fluid. For liquids bordering a solid surface, an equation is obtained that implicitly considers all irreducible diagrams.

The electronic system of molecular-based magnets is promising for use in quantum computing devices. Magnetic resonance techniques are used for magnetization manipulation and coherence tracking. The complexes [n-Bu₄N]₂[Cu(opba)] and [n-Bu₄N]₂[Ni(opba)] have been studied by ¹H NMR technique using different pulse protocols. It is shown that the interpulse delay shift and phase cycling approaches are applicable in ¹H NMR, but it’s not as efficient as they are in EPR. Since many nuclei positions completely suppress the unwanted echo contribution, the subensembles including the longitudinal magnetization evolution should be considered.

The ¹H, ¹³C, ¹¹B and ²⁷Al NMR signals of several polycyclic spiro-fused terpene-alumolanes and spiro-fused terpene-borolane were assigned. Aluminolanes form the dimers predominantly at the cyclic Al(1)–C(5) bond in toluene according to DFT calculations of Gibbs free energy of dimerization reaction and ²⁷Al NMR spectroscopy (δ_Al ∼ 150–159 ppm). In tetrahydrofuran, the complexation of a solvent molecule on aluminolane metal atom proceeds, as evidenced by the shift of signals in the ²⁷Al NMR spectra to δ_Al ∼ 174–178 ppm. The signals of methylene groups located in α-position relative to aluminum and boron atoms are broadened or not observed in ¹H and ¹³C NMR spectra because of quadrupole relaxation of these heteroatoms. Theoretical conformational analysis showed that the energy barrier for inversion of terpene derivatives of spiro-fused 1-fluoroborolane is lower compared to those of spiro-fused 1-ethylalumolanes.

The authors study the effect a PMN‒PT ([Pb(Mg_1/3Nb_2/3)O₃]_0.7‒[PbTiO₃]_0.3) piezoelectric substrate has on the superconducting properties of a Co1/Cu/Co2/Cu/Pb thin-film heterostructure. A change in temperature T_c of the superconducting transition in electric and magnetic fields is detected. The maximum difference between T_c values is found to be 15 mK in an applied electric field of 1 kV/cm. In an external magnetic field, the greatest T_c difference is more than 80 mK upon changing the mutual orientation of the magnetizations of ferromagnetic layers from collinear to perpendicular.

The authors study the formation of crystals of Fe-Ga oxides and Fe–Ga–Cu borates in a multicomponent flux system based on Bi₂Mo₃O₁₂–Na₂B₄O₇. The Curie–Weiss temperature (θ_CW = 289 K) and the temperature of the ferrimagnet–paramagnet phase transition (T_C = 288 K) are determined from the electron spin resonance (ESR) spectrum and the magnetization of an Fe_1.1Ga_0.9O₃ single crystal, depending on temperature. Lines of spin-wave resonance are observed in the spectrum of magnetic resonance in the ordered phase.