Новые публикации

https://doi.org/10.1007/s10948-024-06890-8

The phenomenon of shape anisotropy predominantly constitutes the principal factor influencing effective anisotropy, serving as a significant determinant of the magnetic characteristics of one-dimensional ferromagnetic nanostructures, materials that hold substantial promise for a diverse array of applications in the domains of electronics and biomedicine. However, it is noteworthy that effective anisotropy may be modulated through the manipulation of various other forms of anisotropy, thereby facilitating the tuning of the magnetic properties of nanowire arrays without necessitating alterations to their spatial curvature. In this study, we elucidate the characteristics of nanowire arrays with varying lengths and compositions, which have been electrochemically synthesized utilizing identical porous templates. Through a range of experimental methodologies, we establish a correlation between atypical magnetic behavior and the underlying morphology and crystalline structure of the nanowires. We attribute the pronounced magnetostatic interactions observed within cobalt (Co) nanowires to the presence of significant local uniaxial magnetocrystalline anisotropy, along with a nanostructure oriented perpendicular to the longitudinal axis of the nanowire. Furthermore, we examine the repercussions of substantial discrepancies in the lengths of iron (Fe) nanowires on the magnetostatic field distribution. Our analysis employs mean field theory, incorporating the contributions of various anisotropies present within the system, as well as the non-uniform lengths of the nanowires. Ultimately, through micromagnetic simulations, we investigated the stray fields present within the nanowire array and delineated how strong magnetocrystalline anisotropy and the variability in length affect their spatial distribution.

https://doi.org/10.1016/j.molliq.2024.126642

Nematic liquid crystal layers doped with dichroic anthraquinone dyes at the hybrid tangential-conical boundary conditions have been considered under light irradiation. The samples under study are sensitive to the exposure time, light polarization and wavelength that leads to a modification of the optical textures, which persists for a long time. It has been shown this effect is caused by a dye-initiated change in the director tilt angle at the conical-anchored substrate. The results obtained are of interest for the development of liquid crystal sensors with tunable optical characteristics under the influence of low-power light.

https://doi.org/10.1007/s00339-024-08131-0

The development of new materials showing the magneto-caloric effect (MCE) requires fast and reliable characterization methods. For this purpose, a phenomenological model developed by M. A. Hamad has proven to be a useful tool to predict the magnetocaloric properties (the isothermal magnetic entropy change, Δ�M, the magnetization-related change of the specific heat, Δ��,�, and the relative cooling power, RCP) via calculation from magnetization measurements as a function of temperature, M(T). However, fitting the M(T) data is difficult for broad, smoothed-out transition curves which are often observed for material systems such as core-shell nanoparticles, nanowires, nanowire fabrics or nanoparticle hybrid materials. Thus, in this contribution we present a different approach enabling proper fitting of such magnetization data via the use of an asymmetric Boltzmann sigmoid function, which provides a clear physical background and enables to properly describe the broad and smoothed out transitions of nanomaterials. As examples for our procedure, we present fits to M(T) curves of polycrystalline, bulk La0.67Ba0.33MnO3 as well as La1−�Sr�MnO3 (�= 0.2, 0.3, 0.4) and La0.7Ca0.3MnO3 nanostructured materials from various authors.

https://doi.org/10.1016/j.solidstatesciences.2024.107799

The analysis of baro- and piezo-caloric effects in ferroelectrics and ferroelastics containing tetrahedral and octahedral ion groups in the structure is carried out. The role of the degree of structural disorder in the formation of both effects is discussed. The features of the caloric response at phase transitions of different proximity to the tricritical point are revealed. The strong piezocaloric anisotropy of the studied materials is a convenient tool for extending the operating temperature range of the cooling cycle. An important advantage of ferroelastics and ferroelectrics undergoing transformations of the first order is the combination in one material of low thermal hysteresis and high sensitivity to hydrostatic and/or uniaxial pressure.

https://doi.org/10.1007/s10948-024-06835-1

In this manuscript we study the magnetic MAOX phases (M = Mn, Cr; A = Ga, Al, X = C) obtained by the replacement of the A-layer in the parent MAX phase by the AO₂ layer. The screening analysis of the magnetic and electronic properties of Mn- and Cr-based MAOX phases is performed using DFT calculations. All MAOX are thermodynamically stable. It was found that in MAOX phases Cr magnetic moments are pronounced increased in compare to corresponding MAX phase. Moreover, drastically changes in the electronic structure arise in Cr₂AlO₂C and Cr₂GaO₂C MAOX phases. The metal behavior in Cr₂GaC MAX phase changes for the near to half-metallic behavior with 90% spin polarization at the Fermi energy in Cr₂GaO₂C MAOX phases. We have found that in Cr₂AlO₂C, the change in the electronic structure leads to the formation of the spin-gapless semiconductor state under slight extension in the ab plane. The obtained results make Cr₂GaO₂C and especially Cr₂AlO₂C prospective candidates for application as functional elements of electronics and spintronics. 

https://doi.org/10.1016/j.jallcom.2024.177925

The effect of nonstoichiometry in manganese selenide (MnSe)_1х(Tm_0.76Se)_х (0 ≤ x ≤ 0.3) substituted with thulium of variable valence on the magnetic, structural, and magnetoelastic properties of the compound has been studied. The magnetic susceptibility in the temperature range of 801000 K, infrared spectra (IR) in the frequency range of 4007500 cm^–1 at temperatures of 80500 K, thermal expansion coefficient, electrostriction, and magnetostriction of the compound have been experimentally determined. The maximum paramagnetic susceptibility, thermal expansion coefficient, and IR absorption frequency shift and the critical temperatures and frequencies at which the IR absorption vanishes have been found above the Néel temperature. A model of bipolarons with vacancies in the anion subsystem has been proposed. Anomalies in the magnetic and structural characteristics of the investigated compound have been explained by the bipolaron dissociation accompanied by a singlettriplet transition and vacancy recombination. The temperatures of the onset of the piezoelectric effect and magnetostriction induced by the loss of inversion in clusters with thulium and the formation of ferromagnetic exchange between thulium and manganese ions have been established. It is shown that the negative thermal expansion coefficient is caused by the competition of the ferro- and antiferromagnetic interactions.

https://doi.org/10.1016/j.vacuum.2024.113877

The problem under study is concerned with amorphous silicon (a-Si) crystallization which is induced by an intermetallic compound, with this compound chosen to be Al₂Cu, formed by a solid-state reaction between nanolayers of aluminum and copper in a Cu/Al/a-Si multilayer system. In the case of crystallization initiated by the intermetallic compound Al₂Cu, the crystallization temperature of amorphous silicon was found to be ≈ 300°С (upon heating at a rate of 5–10 °C/min), which was significantly higher than in the case of pure Al (≈170°С), but lower as compared to using pure Cu (≈485°С). The higher crystallization temperatures in comparison with aluminium-induced crystallization are assumed to be caused by a decrease in the number of free electrons due to the presence of copper and formation of the Al₂Cu phase. By kinetic modeling, it was revealed that the mechanism of a-Si crystallization induced by the intermetallic compound Al₂Cu was similar to the mechanism of Al-induced crystallization of a-Si in multilayer (Al/a-Si)_n films, i.e the process of a-Si crystallization occurred in two subsequent stages: Cn-X→Fn. Kinetic parameters of silicon crystallization for each reaction step were obtained. The enthalpy of a-Si crystallization initiated by Al₂Cu was estimated to be ΔH = 12.3 ± 0.5 kJ/mol.

https://doi.org/10.1016/j.marpolbul.2024.117375

This work reports on the first multi-scale NMR study of new plant-based herding agent suitable for application in Arctic marine environment. Using NMR spectroscopy the chemical components of the herding agent were established while through the NMR relaxometry and diffusometry the local dynamics, molecular mobility, and transport properties of the components were studied depending on water content upon dilution. MRI method was first applied to probe the effect of herder on freezing and thawing processes occurring in dodecane/water and light oil/water mixtures. It was found out that the herder affects the internal structure and the surface texture of the ice under oil slick, and presence of herder is supposed to shift the heat balance in marine freeze/thawing cycling inherent to cold regions. The results of the work contribute into better understanding of the surfactant-oil/water/ice interaction and facilitate more effective application of herders for oil spills response in marine environment.

https://doi.org/10.1007/s11433-024-2496-9

Bound states in the continuum (BICs) are perfectly localized resonances despite embedding in the continuum spectrum. However, an isolated BIC is very sensitive to the structure perturbation. Here, we report merging acoustic BICs in a single open resonator, robust against the structure perturbation. We find that both symmetry-protected BIC and Friedrich-Wintgen BIC are sustained in a single coupled waveguide-resonator system. By varying the height and length of the resonator, these two BICs move toward each other and merge into a single one at a critical dimension. Compared to an individual BIC, the merged BIC is robust against fabrication error because its Q-factor is proportional to ΔL⁻⁴, where ΔL embodies the structure perturbation. The essence of this extraordinary phenomenon is perfectly explained by the two- and three-level approximations of the effective non-Hermitian Hamiltonian. Finally, we present direct experimental demonstrations of the moving and merging of BICs in a coupled 3D waveguide-resonator, which are evidenced by the vanishing of the linewidth of Fano resonance in the transmission spectra. Our results may find exciting applications in designing high-quality acoustic sources, sensors and filters.

https://doi.org/10.1016/j.chemphys.2024.112528

The work elucidates detailed analysis of X-ray near edge structure of Gd³⁺ ions using Synchrotron studies and deciphers the energy transfer mechanism involved in the stoichiometric ratio of (79-x)B₂O₃ + 10ZnO + 10BaO + xGd₂O₃ + 1Sm₂O₃ (BZBGS; x  = 0, 5, 10, 15, 20 mol.%) glasses. A detailed analysis of the glasses’ optical, structural, and luminescence properties were instigated to understand light emitting and scintillating behaviour. The oxidation state of Gd atom inside the glass found to be + 3. Stimulated emission cross section, radiative transition probability and branching of the metastable state of rare-earth ions were evaluated using Judd-Ofelt model and compared with other reported literature. Photo-Emission spectra were monitored at the UV-C band and X-rays. Luminescence was analysed with various excitation wavelengths and sources. Photoluminescence quantum yield show more than 22 % efficiency and show more than 15 % compared with other reported glasses. Luminescence intensity ratio was analysed and found that the Sm³⁺-ions do not occupy the inversion-symmetry which enhances the luminescence intensity in the present glass system. The CIE and CCT values were evaluated and discussed.

https://doi.org/10.1016/j.matlet.2024.137744

For the first time Ni₄₄Fe₁₉Ga₂₇Co₁₀ single crystals with high-temperature martensitic transformation (M_s = 336 K) and high-temperature superelasticity (373–548 K) under tension and compression were obtained after annealing at 1448 K for 6 h, followed by fast quenching in ice-cold salt water. The increase in temperature is associated with the precipitation of the large γ-particles and the substantial decrease in the precipitation of the nanosized ω-phase, which was observed in the single crystals after annealing at 1448 K for 1 h with slower water quenching.

https://doi.org/10.1016/j.jmmm.2024.172675

The interplay of the magnetically dead layer and structural defects in interacting ultrafine nickel ferrite (NiFe₂O₄) nanoparticles (<d> = 4 nm) have been investigated using transmission electron microscopy, X-ray diffraction, ⁵⁷Fe Mössbauer spectrometry, and static (dc) magnetization and dynamic (ac) susceptibility measurements. According to the magnetic measurement data, there are three magnetic subsystems in NiFe₂O₄ nanoparticles. The first subsystem with the lowest blocking (spin freezing) temperature (T_S = 8 K) involves atomic magnetic moments of magnetically disordered particles with a size of d < 4 nm. The other two subsystems are formed by magnetic moments of the cores of nanoparticles more than 4 nm in size and by correlated surface spins in nanoparticle clusters. The magnetic moments of the ferrimagnetically ordered cores are blocked at a higher temperature (∼40 K). It has been shown that the most significant contribution to the energy dissipation is made upon blocking of the correlated nanoparticle surface spins from the magnetically dead layer on the nanoparticle surface. The magnetic measurements have shown that the thickness of this layer is d_md ≈ 1 nm for a particle with a diameter of < d> = 4 nm. At the same time, the ⁵⁷Fe Mössbauer spectrometry study has revealed a structural disorder penetrating to a depth of up to d_cd ≈ 0.6 nm in a particle with a diameter of < d> = 4 nm. This evidence for a faster violation of the magnetic order than in the case of the crystal order upon moving away from the center of a particle to its periphery.

https://doi.org/10.1016/j.physb.2024.416754