New Publications

Fractal Dimension Effect on the Magnetization Curves of Exchange-Coupled Clusters of Magnetic Nanoparticles

Komogortsev, S. V.; Iskhakov, R. S.; Fel'k, V. A. Source: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 128 (5):754-760; 10.1134/S1063776119040095 MAY 2019

The effect of the fractal dimension of exchange-coupled clusters of magnetic nanoparticles on their magnetization curves is predicted by scaling estimates. These predictions form the basis for the experimental technique used for determining the fractal dimension of nanoparticle clusters from the magnetization curves. We estimate the reliability of determining the dimension by such methods with the help of micromagnetic simulation. It is shown that the effective dimension of magnetic correlation volumes, which is determined from analysis of the magnetization approaching saturation, is in conformity with the dimension of fractal clusters determined from analysis of their morphology. The dimension estimated from analysis of the coercive field on the particle size in a physically natural situation of the dipole–dipole interaction between nanoparticles provides estimates of the cluster dimension, which strongly differs from estimates obtained from analysis of their morphology.

Nematic and Cholesteric Liquid Crystal Structures in Cells with Tangential-Conical Boundary Conditions

Krakhalev, Mikhail N.; Bikbaev, Rashid G.; Sutormin, Vitaly S.; Timofeev, Ivan, V; Zyryanov, Victor Ya Source: CRYSTALS, 9 (5):10.3390/cryst9050249 MAY 2019

Orientational structures formed in nematic and cholesteric layers with tangential-conical boundary conditions have been investigated. LC cells with one substrate specifying the conical surface anchoring and another substrate specifying the tangential one have been considered. The director configurations and topological defects have been identified analyzing the texture patterns obtained by polarizing microscope in comparison with the structures and optical textures calculated by free energy minimization procedure of director field and finite-difference time-domain method, respectively. The domains, periodic structures and two-dimensional defects proper to the LC cells with tangential-conical anchoring have been studied depending on the layer thickness and cholesteric pitch

Optical and calorimetric studies of K2TaF7

Mel'nikova, Svetlana, V; Bogdanov, Evgeniy, V; Molokeev, Maxim S.; Laptash, Natalia M.; Flerov, Igor N. Source: JOURNAL OF FLUORINE CHEMISTRY, 222 75-80; 10.1016/j.jfluchem.2019.04.016 JUN 2019

Optical and calorimetric experiments on K2TaF7 are performed in a wide temperature range. No features were found in the behavior of the birefringence Δnb(T), the angle of rotation of the indicatrix ϕ(T) and the heat capacity ΔCp(T) except for those associated with the PnmaP21/c phase transition. Structural transformation was characterized as strong first order “proper” ferroelastic accompanied by a huge angle ϕ ≈40° and strong pre-transition phenomena in Δnb(T). Two contributions to the anomalies of the optical properties were found associated with the photoelastic effect and the transition parameter related linearly to the spontaneous deformation. Thermal treatments cause correlated changes in temperature and enthalpy of the phase transition, which leads to the invariance of the large magnitude of the corresponding entropy ΔS = 22 J/mol·K which does not match the model with the absence of structural disorder in the Pnma phase.

Understanding perceived color through gradual spectroscopic variations in electrochromism

Mishra, Suryakant; Yogi, Priyanka; Chaudhary, Anjali; Pathak, Devesh K.; Saxena, Shailendra K.; Krylov, Alexander S.; Sagdeo, P. R.; Kumar, Rajesh Source: INDIAN JOURNAL OF PHYSICS, 93 (7):927-933; 10.1007/s12648-018-1353-7 JUL 2019

A bias-dependent in situ Raman scattering and UV–Vis absorption spectroscopic change has been correlated with the corresponding color change of an electrochromic device in an attempt to explain how to understand the relationship between actual perceived color and its absorption/transmittance spectra. For this, the bias across an electrochromic device was increased gradually, rather than abruptly turning ON and OFF, to see subtle variations in Raman and absorption spectra due to bias. Raman scattering establishes that viologen changes its oxidation state reversibly between two redox species (EV2+ to EV+•) as a result of bias-induced dynamic redox process. A gradual variation in Raman and absorption spectra, which shows maximum absorption corresponding to the yellow light, accompanies similar variation in color change of the device as visible by naked eye. These spectroscopic results are correlated with the perceived blue color, in the reflected light, by the eye to understand the actual reason behind this. Maximum absorption of yellow light by the device resulting in blue appearance has been explained using the concept of additive and subtractive primary colors.

Brownian dynamics of the self-assembly of complex nanostructures in the field of quasi-resonant laser radiation

Kornienko, Victoria S.; Tsipotan, Aleksey S.; Aleksandrovsky, Aleksandr S.; Slabko, Vitaliy V. Source: PHOTONICS AND NANOSTRUCTURES-FUNDAMENTALS AND APPLICATIONS, 35 10.1016/j.photonics.2019.100707 JUL 2019

Self-assembly of nanoparticles under the action of laser field can be an universal method for the formation of nanostructures with specific properties for application in sensorics and nanophotonics. For prognosis of the self-assembly processes, the model of movement of an ensemble of nanoparticles in a viscous media under the action of laser radiation with the account for interaction of laser-induced polarizations and Brownian dynamics is developed. This model is applied to the investigation of the self-assembly process of a triple of nanoparticles into three-particle structure with a predetermined geometry.Two specific cases of formation of nanostructure from a preliminarily formed pair of particles are studied: either for the pair fixed in space or from the unfixed pair of nanoparticles. The geometry of resulting nanostructures is shown to be determined by the polarization direction of laser radiation and the laser wavelength. Under proper choice of these parameters the formation of structures is shown to be highly efficient. E. g., maximum probability of structures formation is as hig as 36–46% per single laser pulse of 10 ns duration.

Phase transitions in Rb2KLuF6 crystal

Krylov, A. S.; Vtyurin, A. N.; Voronov, V. N.; Krylova, S. N. Source: FERROELECTRICS, 538 (1):28-34; 10.1080/00150193.2019.1569982 2019

The Raman spectra of Rb2KLuF6 elpasolite crystal have been studied in a wide temperature range, including two phase transitions: from the cubic phase to the tetragonal phase and then to the monoclinic phase. The results of an analysis of the temperature dependences of the parameters of spectral lines are in good agreement with the thermodynamic data on the phase transitions. The analysis of Raman spectra shows that the transition from cubic to tetragonal phase is a second-order transition and the transition from the tetragonal to the monoclinic phase is a weak first-order transition.

Thermal expansion and polarization of (1-x)PNN-xPT solid solutions

Gorev, M. V.; Flerov, I. N.; Bormanis, K.; Kalvane, A. Source: INTEGRATED FERROELECTRICS, 196 (1):60-63; SI 10.1080/10584587.2019.1591957 FEB 12 2019

The paper presents the results of detailed studies of the thermal expansion of (1-x)PbNi1/3Nb2/3O3-xPbTiO3 solid solutions with x = 0-0.8. The anomalous and lattice contributions to deformation and the thermal expansion coefficient are analyzed and the mean square polarization Pd is determined. The results obtained are discussed within the framework of the thermodynamic theory and the Landau 2-4-6 coefficients for solid solutions are estimated.

Toroidal Configuration of a Cholesteric Liquid Crystal in Droplets with Homeotropic Anchoring

Krakhalev, M. N.; Rudyak, V. Yu.; Gardymova, A. P.; Zyryanov, V. Ya. Source: JETP LETTERS, 109 (7):478-481; 10.1134/S0021364019070075 APR 2019

Orientational structures formed in cholesteric droplets with homeotropic surface anchoring have been studied by means of polarization optical microscopy and computer simulations. It has been found that, when the ratio of the size of droplets to the pitch of a cholesteric helix ranges from 1.4 to 2.9, an axisymmetric toroidal cholesteric structure is formed with a topological linear defect in the form of an equatorially located surface ring. The features of the toroidal structure in cholesteric droplets and their optical textures for various observation schemes are examined in detail.

The Influence of the Interface on the Magnetic State in Two-Layer Films of the Fe-Bi System

Patrin, G. S.; Yakovchuk, V. Yu; Yarikov, S. A.; Shiyan, Ya G.; Furdyk, V. P. Source: TECHNICAL PHYSICS LETTERS, 45 (5):507-510; 10.1134/S1063785019050262 MAY 2019

Results of the experimental investigation of two-layer films in the Fe–Bi system are presented. It is found that the order of sequential deposition of the magnetic and nonmagnetic layers influences both the character of magnetization process and the magnetic resonance behavior. The obtained results are explained by the formation of a strongly anisotropic sublayer of nanogranular iron in the Bi/Fe film structure.

A Highly Selective Bandpass Filter Based on Suspended Substrate Resonators with a Two-Sided Stripline Pattern

Belyaev, B. A.; Serzhantov, A. M.; Bal'va, Ya. F.; Leksikov, An. A.; Grushevskii, E. O. Source: TECHNICAL PHYSICS LETTERS, 45 (5):485-488; 10.1134/S1063785019050225 MAY 2019

New resonator design employing a hairpin stripline conductor with a stub situated on one side of a dielectric substrate and regular stripline conductors (connected to a screen) on the other side. Eigenfrequencies of the first three oscillation modes of this resonator can be made closer to each other, so that the resonances of two modes are involved in the formation of the passband while the third mode resonance forms a minimum of the transmission coefficient adjacent to the passband. A structure comprising four resonators of this type has the characteristic of an eighth-order bandpass filter arranged in a case with 45 × 16 × 6.25-mm internal dimensions possessing   f0 = 0.52 GHz central frequency with a 14% relative bandwidth. The filter is highly selective due to the attenuation poles being close to the pass band and a wide high-frequency stopband extending above a fivefold   f0  value at a level of  –100 dB.

Linear Zero Thermal Expansion in a Deep-Ultraviolet Transparent Crystal of BPO4 with Cristobalite-like Structure

Wang, Naizheng; Jiang, Xingxing; Molokeev, Maxim S.; Song, Gaomin; Guo, Shibin; Huang, Rongjin; Li, Laifeng; Wu, Yicheng; Lin, Zheshuai Source: CRYSTAL GROWTH & DESIGN, 19 (6):3109-3112; 10.1021/acs.cgd.9b00361 JUN 2019

We report the discovery of the zero thermal expansion (ZTE) effect in BPO4, a famous deep-ultraviolet (DUV) optical material with cristobalite-like structure. It is revealed that BPO4 has a linear ZTE coefficient of −0.16(5) MK–1 along the c-axis as temperature increases from 13 to 300 K, which originates from the subtle counterbalance between the rotation-induced expansion and contraction effects among BO4 and PO4 groups. BPO4 is a unique DUV cristobalite-like material exhibiting the linear ZTE behavior.

Study of the Physical Properties and Electrocaloric Effect in the BaTiO3 Nano- and Microceramics

Kartashev, A. V.; Bondarev, V. S.; Flerov, I. N.; Gorev, M. V.; Pogorel'tsev, E. I.; Shabanov, A. V.; Molokeev, M. S.; Guillemet-Fritsch, S.; Raevskii, I. P. Source: PHYSICS OF THE SOLID STATE, 61 (6):1052-1061; 10.1134/S1063783419060088 JUN 2019

The specific heat, thermal expansion, permittivity, and electrocaloric effect in bulk of BaTiO3 (BT) samples in the form of nano- (nBT-500 nm) and micro- (mBT-1200 nm) ceramics fabricated using spark plasma sintering and solid-state plasma techniques have been investigated. The size effect has been reflected, to a great extent, in the suppression of the specific heat and thermal expansion anomalies and in the changes in the temperatures and entropies of phase transitions and permittivity, and a decrease in the maximum intensive electrocaloric effect: ΔTmaxAD = 29 mK (E = 2.0 kV/cm) for nBT and ΔTmaxAD = 70 mK (E = 2.5 kV/cm) for mBT. The conductivity growth at temperatures above 360 K leads to the significant irreversible heating of the samples due to the Joule heat release in the applied electric field, which dominates over the electrocaloric effect.

Influence of the Coulomb Repulsions on the Formation of the Superconducting Gap of the Spin-Polaron Quasiparticles in Cuprates

Val'kov, V. V.; Korovushkin, M. M.; Barabanov, A. F. Source: JOURNAL OF LOW TEMPERATURE PHYSICS, 196 (1-2):242-252; 10.1007/s10909-018-02120-3 JUL 2019

Taking into account the real crystalline structure of the CuO2 plane and the strong spin-fermion coupling, the influence of the on-site Coulomb repulsion of holes Up and the intersite Coulomb repulsion V2 between holes located at the next-nearest-neighbor oxygen ions on the formation of the superconducting gap with the d-wave symmetry of the order parameter of the spin-polaron quasiparticles is studied. It is shown that the formation of the resulting superconducting gap within the spin-fermion model is caused by three components. The dependence of the narrowing of the superconducting gap on the values Up and V2 is analyzed.

Formation of the magnetic subsystems in antiferromagnetic NiO nanoparticles using the data of magnetic measurements in fields up to 250 kOe

Popkov, S., I; Krasikov, A. A.; Velikanov, D. A.; Kirillov, V. L.; Martyanov, O. N.; Balaev, D. A. Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 483 21-26; 10.1016/j.jmmm.2019.03.004 AUG 1 2019

It is well-known that the fraction of surface atoms and the number of defects in an antiferromagnetic particle increase with a decrease in the particle size to tens of nanometers, which qualitatively changes the properties of the particle. Specifically, in antiferromagnetic nanoparticles, spins in the ferromagnetically ordered planes can partially decompensate; as a result, an antiferromagnetic particle acquires a magnetic moment. As a rule, uncompensated chemical bonds of the surface atoms significantly weaken the exchange coupling with the antiferromagnetic particle core, which can lead to the formation of an additional magnetic subsystem paramagnetic at high temperatures and spin-glass-like in the low-temperature region. The existence of several magnetic subsystems makes it difficult to interpret the magnetic properties of antiferromagnetic nanoparticles. It is shown by the example of NiO nanoparticles with an average size of 8 nm that the correct determination of the contributions of the magnetic subsystems forming in antiferromagnetic nanoparticles requires magnetic measurements in much stronger external magnetic fields than those commonly used in standard experiments (up to 60–90 kOe). An analysis of the magnetization curves obtained in pulsed magnetic fields up to 250 kOe allows one to establish the contributions of the uncompensated particle magnetic moment μun, paramagnetic subsystem, and antiferromagnetic particle core. The μun value obtained for the investigated NiO particles is consistent with the Néel model, in which μun ∼ N1/2 (N is the number of magnetically active atoms in a particle), and thereby points out the existence of defects on the surface and in the bulk of a particle. It is demonstrated that the anomalous behavior of the high-field susceptibility dM/dH of antiferromagnetic NiO nanoparticles, which was observed by many authors, is caused by the existence of a paramagnetic subsystem, rather than by the superantiferromagnetism effect.

Exponential Bound for the Heating Rate of Periodically Driven Spin Systems

Zobov, V. E.; Kucherov, M. M. Source: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 128 (4):641-649; 10.1134/S1063776119030130 APR 2019

For the nuclear spin system of a solid in the presence of an inhomogeneous magnetic field, we have found a rigorous bound for the heating rate of the system under the action of a high-frequency magnetic field, which is applied, for example, to create effective Hamiltonians. We consider the autocorrelation function (ACF) of a spin rotating in a local field whose fluctuations are specified by a Gaussian random process. The correlation function of a random field is taken as the sum of a static inhomogeneous contribution and a time-dependent contribution expressed self-consistently via the spin ACF. The ACF singularities on the imaginary time axis whose coordinates determine the exponents of exponential asymptotics in the high-frequency domain are investigated. The dependences of the coordinates on field inhomogeneity for various approximations have been derived. The wing of the ACF spectrum in the cumulant approximation is shown to serve as a rigorous upper bound for the wing of the ACF spectrum and, consequently, for the heating rate of the system when subjected to variable magnetic fields. We have established that randomly distributed inhomogeneous magnetic fields increase the wings of the ACF spectra and, thus, speed up the system’s heating.

Structural, Magnetic, and Thermodynamic Properties of Ordered and Disordered Cobaltite Gd0.1Sr0.9CoO3-

Dudnikov, V. A.; Kazak, N. V.; Orlov, Yu. S.; Vereshchagin, S. N.; Gavrilkin, S. Yu.; Tsvetkov, A. Yu.; Gorev, M. V.; Veligzhanin, A. A.; Trigub, A. L.; Troyanchuk, I. O.; Ovchinnikov, S. G. Source: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 128 (4):630-640; 10.1134/S1063776119020171 APR 2019

The effect of cationic and anionic orderings on the crystal structure and magnetic properties of substituted rare-earth cobaltites Gd0.1Sr0.9CoO3 – δ was studied using X-ray diffraction, measurement of XANES spectra, and magnetic and thermodynamic characteristics. The effects of ordering cause a decrease in symmetry to tetragonal and a distortion of the coordination octahedra of CoO6. Anomalous magnetic and thermodynamic quantities are observed at 260 and 360 K, respectively, for disordered and ordered samples. The XANES spectra measured at the CoK edge did not reveal a noticeable shift in the absorption edge compared with the spectrum of original GdCoO3. This suggests that the charge compensation process is associated not only with a change in the electronic state of cobalt ions, but also with the emergence of holes in the 2p states of oxygen.

London Penetration Depth as a Test of Order Parameter Symmetry in Sodium Cobaltate Superconductors

Dzebisashvili, Dmitry M.; Klyuchantsev, Andrey B. Source: SYMMETRY-BASEL, 11 (5):10.3390/sym11050633 MAY 2019

Temperature dependence of the magnetic field penetration depth λ was calculated for water intercalated sodium cobaltate superconductor Na x CoO 2y H 2 O. Assuming that the system is in the chiral d+id–wave superconducting state, it was shown that the shifting of the excitation spectrum nodal points off the normal phase Fermi surface due to variation of the sodium content x changes the functional form of the temperature dependence of λ2 from exponential to linear in the low temperatures region. It is argued that this change in the functional form of T–dependence of the λ2 can serve as a proof for the chiral symmetry of the superconducting order parameter in the sodium cobaltate.

Lead-Free Perovskite Derivative Cs2SnCl6-xBrx Single Crystals for Narrowband Photodetectors

Zhou, Jun; Luo, Jiajun; Rong, Ximing; Wei, Peijia; Molokeev, Maxim S.; Huang, Yang; Zhao, Jing; Liu, Quanlin; Zhang, Xiuwen; Tang, Jiang; Xia, Zhiguo Source: ADVANCED OPTICAL MATERIALS, 7 (10):10.1002/adom.201900139 MAY 2019

Lead‐free and stable Sn halide perovskites demonstrate tremendous potential in the field of optoelectronic devices. Here, the structure and optical properties of the “defect” perovskites Cs2SnCl6−xBrx are reported, as well as their use as photodetector materials. Millimeter‐sized Cs2SnCl6−xBrx single crystals are grown by the hydrothermal method, with the body color continuously changing from transparent to yellow and finally to dark red. Narrowband single‐crystal photodetectors using Cs2SnCl6−xBrx crystals are presented, which show a high detectivity of ≈2.71 × 1010 Jones, with narrowband photodetection (full‐width at half‐maximum ≈45 nm) and high ion diffusion barriers. Moreover, the response spectra are continuously tuned from near violet to orange depending on the variation of the bandgap of the single crystals by changing the halide compositions. The strong surface charge recombination of the excess carriers near the crystal surfaces produced by short wavelength light elucidates the narrowband photodetection behavior. This work provides a new paradigm in the design of lead‐free, stable, and high‐performance perovskite derivatives for optoelectronics applications.

A novel red-emitting La2CaHfO6:Mn4+ phosphor based on double perovskite structure for pc-WLEDs lighting

Xing, Gongcheng; Feng, Yuxin; Gao, Zhiyu; Tao, Mengxuan; Wang, Hongquan; Wei, Yi; Molokeev, Maxim S.; Li, Guogang Source: CRYSTENGCOMM, 21 (23):3605-3612; 10.1039/c9ce00556k JUN 21 2019

Non-rare earth doped oxides with red emission are one of the current research hotspots for achieving the warm white light range in the phosphor converted white light emitting diodes (pc-WLEDs) field. In the current work, a novel Mn4+-activated La2CaHfO6 red phosphor is reported for the first time and its crystal structure is analyzed by Rietveld refinement. The photoluminescent properties of La2CaHfO6:Mn4+ are investigated in detail with the help of diffuse refletance spectroscopy, photoluminescence spectroscopy, and temperature-dependent PL spectroscopy. Based on the diffuse refletance spectra, the calculated optical band gap for La2CaHfO6 is 4.9 eV, indicating that La2CaHfO6 could be a suitable host for activators' doping. Under 380 nm near-ultraviolet (n-UV) light excitation, the as-prepared La2CaHfO6:Mn4+ displays intense red emission centered at 693 nm. Through an accurate calculation of Dq/B (2.47) and nephelauxetic effect β1 (0.949), the origination of strong crystal field (CF) and deep-red emission is demonstrated. By combining the representative La2CaHfO6:0.002Mn4+, blue BAM:Eu2+, and green (Ba,Sr)2SiO4:Eu2+ phosphors with a 380 nm UV chip to fabricate the pc-WLEDs device, a white light is obtained with low correlated color temperature (CCT = 5165 K) and high color rendering index (Ra = 87.8), demonstrating that the as-prepared La2CaHfO6:Mn4+ phosphors can be used as red-emitting candidate in pc-WLEDs lighting.

Technological Basis of the Formation of Micromesh Transparent Electrodes by Means of a Self-Organized Template and the Study of Their Properties

Voronin, A. S.; Simunin, M. M.; Fadeev, Yu. V.; Ivanchenko, F. S.; Karpova, D. V.; Tambasov, I. A.; Khartov, S. V. Source: TECHNICAL PHYSICS LETTERS, 45 (4):366-369; 10.1134/S1063785019040187 APR 2019

This Letter presents the results of a study of the physical properties of micromesh transparent electrodes on a flexible substrate, obtained using a template in the form of silica layers subjected to controlled cracking. For the first time, a combined approach to the control of parameters of a micromesh structure (crack width and cell size) by varying the pH and the thickness of the sol layer is proposed. Using this approach, transparent electrodes with a surface resistance of 4.1 Ω/sq with a transparency of 85.7% were obtained. Micromesh electrodes are characterized by linear optical transmission in the visible and IR ranges, which opens up prospects for their use in optoelectronics.

Experimental Analysis and Empirical Model of the Complex Permittivity of Five Organic Soils at 1.4 GHz in the Temperature Range From-30 degrees C to 25 degrees C

Mironov, Valery L.; Kosolapova, Liudmila G.; Fomin, Sergey V.; Savin, Igor V. Source: IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, 57 (6):3778-3787; 10.1109/TGRS.2018.2887117 JUN 2019

The dielectric measurements were made for five organic soils taken from the tundra territories of Alaska, Yamal, and Taimyr, with the content of organic matter varying from 35% to 80%. The measurements were carried out in the temperature range from -30 °C to 25 °C, frequencies from 0.45 to 16 GHz and soil moisture from close to zero to the field moisture capacity. The refractive mixing model was applied to fit the measurements of the soil's complex refractive index (CRI) as a function of soil moisture, with the values of temperature being fixed. As a result, a respective dielectric model was developed. The amounts of bound and transient water in the thawed and frozen soils were introduced as parameters of the developed model and derived as a function of temperature and content of soil organic matter. The other parameters which concern the CRIs of soil solids as well as bound, transient, and liquid soil water or ice components were derived as a function of temperature. The errors of the proposed model estimated in terms of the values of normalized root-mean-sqaure error for the real and imaginary parts of the soil complex relative permittivity appeared to be 6%-7% and 23%, respectively. The proposed dielectric model can be applied in active and passive remote sensing, in particular, for the SMOS, SMAP, and Aquarius missions after testing in ground-based experiments.

Photo-orientation of nematic liquid crystal without preliminary cell surface treatment

Shvetsov, Sergey A.; Emelyanenko, Alexander, V; Bugakov, Miron A.; Boiko, Natalia, I; Zyryanov, Victor Ya Source: OPTICAL MATERIALS EXPRESS, 9 (6):2595-2600; 10.1364/OME.9.002595 JUN 1 2019

We propose a simple and effective method of liquid crystal photoalignment that does not require any preliminary treatment of the cell substrates. To this aim, a small amount (0.1 wt %) of azobenzene carboxylic acid is added into the nematic liquid crystal. After filling the liquid crystal cell, a part of the dopant molecules is spontaneously adsorbed and attached to the glass surface by hydrogen bonds. This allows one to switch the boundary conditions of liquid crystal between homeotropic and planar due to the reversible trans-cis photoisomerization.

An effect of reduced S-rich fluids on diamond formation under mantle-slab interaction

Bataleva, Yuliya, V; Palyanov, Yuri N.; Borzdov, Yuri M.; Novoselov, Ivan D.; Bayukov, Oleg A. Source: LITHOS, 336 27-39; 10.1016/j.lithos.2019.03.027 JUL 2019

Experimental study, dedicated to understanding the effect of S-rich reduced fluids on the diamond-forming processes under subduction settings, was performed using a multi-anvil high-pressure split-sphere apparatus in Fe3C-(Mg,Ca)CO3-S and Fe0-(Mg,Ca)CO3-S systems at the pressure of 6.3 GPa, temperatures in the range of 900–1600 °C and run time of 18–60 h. At the temperatures of 900 and 1000 °C in the carbide-carbonate-sulfur system, extraction of carbon from cohenite through the interaction with S-rich reduced fluid, as well as C0-producing redox reactions of carbonate with carbide were realized. As a result, graphite formation in assemblage with magnesiowüstite, cohenite and pyrrhotite (±aragonite) was established. At higher temperatures (≥1100 °C) formation of assemblage of Fe3+-magnesiowüstite and graphite was accompanied by generation of fO2-contrasting melts - metal-sulfide with dissolved carbon (Fe-S-C) and sulfide-oxide (Fe-S-O). In the temperature range of 1400–1600 °C spontaneous diamond nucleation was found to occur via redox interactions of carbide or iron with carbonate. It was established, that interactions of Fe-S-C and Fe-S-O melts as well as of Fe-S-C melt and magnesiowüstite, were С0-forming processes, accompanied by disproportionation of Fe. These resulted in the crystallization of Fe3+-magnesiowüstite+graphite assemblage and growth of diamond. We show that a participation of sulfur in subduction-related elemental carbon-forming processes results in sharp decrease of partial melting temperatures (~300 °C), reducting the reactivity of the Fe-S-C melt relatively to FeC melt with respect to graphite and diamond crystallization and decrease of diamond growth rate.

Magnetic Anisotropy in Thin Films of FePt Detected by the Ferromagnetic Resonance Method

Dmitriev, A., I; Kulikov, A., V; Gilmutdinov, I. F.; Dremova, N. N.; Mazitov, A. A.; Dmitrieva, M. S.; Alekseev, S., I; Myagkov, V. G. Source: JOURNAL OF SURFACE INVESTIGATION, 13 (2):210-214; 10.1134/S102745101902006X MAR 2019

FePt thin films are made via the heat treatment of structures containing Pt (001) and Fe (001) epitaxial layers. X-ray spectral analysis and field-emission scanning electron microscopy show that the samples contain the cubic L12–Fe3Pt phase and the tetragonal L10–FePt phase. The magnetic anisotropy of the thin films is studied by ferromagnetic resonance and magnetometric methods. The contributions from the cubic and tetragonal phases to the ferromagnetic-resonance spectrum of the sample are distinguished. The key characteristics of thin films which determine their practical applicability are determined: the Gilbert damping parameter G ~ 0.4, the first and second crystal anisotropy constants K1⊥ = –4.08 × 106 erg/cm3, K2⊥ = 1.34 × 106 erg/cm3, K2|| = –9.76 × 104 erg/cm3.

Weak Ferromagnetism along the Triad Axis and the Basal Anisotropy Caused by the Dzyaloshinskii-Moriya Interaction and the Cubic Electric Field of the FeBO3 Crystal

Ovchinnikov, S. G.; Rudenko, V. V.; Vorotynov, A. M. Source: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 128 (3):443-449; 10.1134/S1063776119020110 MAR 2019

Based on the spin Hamiltonian and taking into account the cubic invariant of the crystal field and the Dzyaloshinskii–Moriya interaction, the weak ferromagnetic moment along the triad axis and the basal anisotropy of FeBO3 crystals are calculated in the approximation of second-order perturbation theory.

Manifestations of Structural Phase Transitions in a Rb2KLuF6 Crystal in Its Raman Spectra

Krylov, A. S.; Vtyurin, A. N.; Voronov, V. N.; Krylova, S. N. Source: OPTICS AND SPECTROSCOPY, 126 (4):341-345; 10.1134/S0030400X1904012X APR 2019

The Raman spectra of an Rb2KLuF6 crystal are studied in the temperature range from 8 to 375 K, which includes two phase transitions: one of which proceeds from a cubic to a tetragonal phase, while the other transition takes place from a tetragonal to a monoclinic phase. An analysis of the temperature dependences of parameters of spectral lines shows that the former transition is of the second kind, while the latter transition is of the first kind, close to the tricritical point. It is shown that the structural phase transitions in the Rb2KLuF6 double perovskite are not associated with disordering. The former transition is associated with rotations of LuF6 octahedra around the fourth-order axis, while the latter transition is related with rotations of octahedra and displacements of rubidium ions.

Macro- and Nanoscale Magnetic Anisotropy of FeNi(P) Micropillars in Polycarbonate Membrane

Komogortsev, S. V.; Chekanova, L. A.; Denisova, E. A.; Bukaemskiy, A. A.; Iskhakov, R. S.; Mel'nikova, S. V. Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (4):911-916; 10.1007/s10948-018-4772-y APR 2019

Macroscopic and local magnetic anisotropy of the FeNi(P) pillars deposited using electroless plating in the pores of the nuclear track-etched polycarbonate membrane has been studied. The alloy fills the pores and forms a nail-shaped pillar. The macroscopic easy magnetization axis was found to be perpendicular to the membrane plane due to magnetic shape anisotropy. The macroscopic magnetic anisotropy constant decreases with decreasing pillar diameter from 0.4 to 0.1 μm supposedly due to increase of the pillar cap contribution. Approach to magnetic saturation analysis indicates that the order in local easy magnetization axis is localized on a nanoscale. The correlation length of the local easy axis and the local magnetic anisotropy field in (Fe100−xNix)98P2 pillars of different compositions with diameter of 0.4 μm are studied.

Anisometric Iron Oxide-Based Nanoparticles and Sols Based on Them: Preparation and Properties

Stolyar, S. V.; Bayukov, O. A.; Chekanova, L. A.; Gerasimova, Y. V.; Sokolov, A. E.; Iskhakov, R. S.; Yaroslavtsev, R. N.; Volochaev, M. N.; Artemyeva, A. S.; Cheremiskina, E. V.; Knyazev, Y. V. Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (4):971-975; 10.1007/s10948-018-4784-7 APR 2019

We have synthesized magnetic powders of the magnetite-maghemite series by the chemical reaction of the FeSO4 iron salt and the natural arabinogalactan polysaccharide. These particles with a high magnetization value (∼ 300 Gs) represent a mixture of spherical particles and nanorods. Particles of a spherical shape (diameter of ∼ 5–6 nm) show a superparamagnetic behavior at room temperature, while rods with a diameter of ∼ 5 nm and a length of 30 nm are magnetic. We have prepared sol samples based on the nanoparticle aqueous solution of arabinogalactan. Our results on the magnetism of the circular dichroism (MCD) on sol are consistent with the of Mössbauer spectroscopy data.

Two-Magnon Relaxation Processes in Nanocrystalline Thin Magnetic Films

Izotov, A. V.; Belyaev, B. A.; Solovev, P. N.; Boev, N. M. Source: RUSSIAN PHYSICS JOURNAL, 61 (12):2313-2320; 10.1007/s11182-019-01673-4 APR 2019

Numerical analysis of the micromagnetic model was used to reveal the ‘resonance’ feature of relaxation processes in nanocrystalline thin magnetic films. This feature manifests itself in the form of sharp broadening of the ferromagnetic resonance (FMR) line at a certain frequency f1 depending on magnetic characteristics of the film, and is observed only in films the thickness of which exceeds some threshold value dmin. Sharp broadening of the FMR line is accompanied by significant shift of the resonance field, whereas the shift value changes the sign at frequency ~ f1. It was shown analytically that the nature of observed effects is associated with the two-magnon process of spin waves scattering on quasi-periodic magnetic microstructure – magnetization ‘ripple’. Obtained expressions for the threshold value of film thickness dmin and frequency of maximum broadening of FMR line f1 agree well with the results of numerical computation of micromagnetic model.

On Nature of the Induced Anisotropy in the Chemically Deposited Co-P Films

Chzhan, Anatoly V.; Podorozhnyak, Sergey A.; Volochaev, Mikhail N.; Patrin, Gennady S. Edited by: Perov N; Semisalova A Source: MOSCOW INTERNATIONAL SYMPOSIUM ON MAGNETISM (MISM 2017), 185 10.1051/epjconf/201818503012 2018

The induced magnetic anisotropy in the Со‒Рfilms prepared by chemical deposition from liquid solutions in a magnetic field has been investigated. The pronounced difference between the anisotropy values and relaxation times points out the existence of different physical mechanisms responsible for the occurrence of anisotropy of the Со‒Р films at low and high pH values. Possible mechanisms of the induced anisotropy in the Со‒Р films prepared at different pH values are discussed.

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