Structural, Dimensional and Thermoelectric Properties of Melt Spun p-Bi0,5Sb1,5Te3

Thermoelectric melt spun p-Bi0,5Sb1,5Te3 powders were obtained and their structural properties were studied. It was established that the crystallites constituting the powder particles are nanofragmented. Powders were compacted by vacuum hot pressing and spark plasma sintering. Thermoelectric characteris-tics of obtained samples were investigated in 100 K-700 K temperature range. The samples prepared by above methods posses low thermal conductivity while retaining values of the Seebeck coefficient and elec-trical conductivity comparable to conventional crystallized materials, thereby thermoelectric efficiency ZT reaches 1.05-1.15 at 330-350 K. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3636

Laser-Induced After-Effect in Tunnel Magnetic Nanostructures

The laser-induced magnetic after-effects in magnetic nanostructures consisting in magnet reversal under ultra-short circularly polarized laser pulses are studied. Using the magneto-optical method and a pump—probe technique based on the Kerr and Faraday effects, features and conditions of magnetic reversal in ferrimagnetic-based nanostructures under femtosecond circularly polarized laser pulses are established. As shown, the mechanisms of such laser-induced impact are a complex process of laser-induced thermal demagnetization of magnetic sublattices with a subsequent magnetic biasing by internal magnetic fields of different nature. Depending on the laser-pulse duration and intensity, they can be effective magnetic fields of laser irradiation or internal magnetic fields conditioned by different rates of the thermal demagnetization of ferrimagnetic sublattices. Features of the laser-induced tunnel magnetoresistance effect in ferrimagnetic junctions are considered.Исследованы лазерно-индуцированные эффекты последействия в магнитных наноструктурах, состоящие в перемагничивании в поле ультракоротких циркулярно поляризованных лазерных импульсов. С использованием магнитооптического метода накачки—зондирования, основанного на эффектах Керра и Фарадея, установлены особенности перемагничивания в ферримагнитных наноструктурах под действием фемтосекундных лазерных импульсов. Показано, что механизмы такого лазерно-индуцированного воздействия являются комплексными процессами лазерно-индуцированного теплового размагничивания магнитных подрешёток с последующим подмагничиванием эффективными внутренними полями различной природы. В зависимости от длительности и интенсивности лазерных импульсов это могут быть поля лазерного излучения или внутренние поля, связанные с различием скоростей теплового размагничивания подрешёток. Рассмотрены особенности лазерно-индуцированного туннельного магниторезистивного эффекта в ферримагнитных переходах.Досліджено лазерно-індуковані ефекти післядії в магнетних наноструктурах, які полягають в перемагнетуванні у полі ультракоротких циркулярно поляризованих лазерних імпульсів. З використанням магнетооптичної методи накачування—зондування, що ґрунтується на Керровому та Фарадейовому ефектах, встановлено особливості перемагнетування у феримагнетних наноструктурах під дією фемтосекундних лазерних імпульсів. Показано, що механізми такого лазерно-індукованого впливу є комплексними процесами лазерно-індукованого теплового розмагнетовування феримагнетних підґратниць з подальшим підмагнетовуванням внутрішніми ефективними полями різної природи. Залежно від тривалости й інтенсивности лазерних імпульсів, це можуть бути поля лазерного випромінення або внутрішні поля, пов’язані з відмінністю швидкостей теплового розмагнетовування підґратниць. Розглянуто особливості лазерно-індукованого тунельного магнеторезистивного ефекту в феримагнетних переходах

The Formation and Study of the FeCo Nanoparticles Alloy in Structure of Metal-Carbon Nanocomposites FeCo/C

The study of the peculiarities of the formation of the nanoparticles FeCo-alloy in the composition of metal-carbon nanocomposites FeCo/C. Structure, phase composition and kinetic processes of synthesis of nanocomposites FeCo/C by methods of Mossbauer spectroscopy were studied. This allowed us to establish the peculiarities of formation of nanoparticles FeCo alloy in the composition of the nanocomposites. The nanocomposites were synthesized by the IR-pyrolysis at temperatures of precursors of 300 - 800 °C on the basis of polyacrylonitrile (PAN), iron acetylacetonate and cobalt acetate. Also it is established that an increase in the average size of nanoparticles FeCo with increasing temperature synthesis is occurred. In the temperature range of synthesis of 600-800 °C the size varies from 9- 10 to 16-18 nm, respectively. The features the phase transitions and phase composition of the metal-carbon nanocomposites FeCo / C were studied by Mossbauer spectroscopy. Nanocomposites were synthesized in the temperature range of T = 300-800 °C. It was shown that the samples synthesized at T = 300 °C contains of superparamagnetic nanoparticles of magnetite and amorphous oxide of iron only. The process of forming nanoparticles of alloy FeCo occurs within the temperature range 500-600 ° C due to the recovery of amorphous iron oxide and magnetite as well as them dissolving in a phase of cobalt. The growth of size of nanoparticles of alloy by agglomeration and dissolution of iron in the alloy nanoparticles occurs only at the temperature range of synthesis 600-800 ° C. This is confirmed by a decrease of the content of Fe, which associated with carbon and it is consistent with the results of phase and structural studies, carried out in previous works

The Structure and Magnetic Properties Metal-carbon Nanocomposites NiCo / C on Based of Polyacrylonitrile

By method of IR-pyrolysis the precursor of polyacrylonitrile and compounds of cobalt and nickel metal-carbon nanocomposites were obtained, representing nanoparticles of alloy NiCo, dispersed in nanocrystal-line carbon matrix. Identification of alloy nanoparticles was carried out by the values of the lattice param e-ter, which was determined by X-ray analysis and was 0,3533 nm (values of the lattice parameter for Ni 0,3529 nm), this corresponds intermetallics Ni0,5Co0,5. By XRD analysis it was determined that an increase in the synthesis temperature of 500 to 800 ºC leads to increase in average size of coherent dissipation of crystallite metal phase. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3632

Features of Formation of the Nanoparticles of Alloys in Metal-carbon Nanocomposites FeCo / C and NiCo / C on Based Polyacrylonitrile

By the method of IR-heating the precursor on base of polyacrylonitrile, compounds of iron, cobalt and nickel metal-carbon nanocomposites were obtained, representing an ensemble of nanoparticles of intermetallic FeCo (NiCo), dispersed in nanocrystalline carbon matrix. XRD analysis revealed that the carbon structure of the PAN-based matrix changed from amorphous to nanocrystalline at the processing temperatures in the range 200-700 °C. Thus there is a reduction of metals from compounds released by degradation of the polymer with hydro-gen. FeCo alloy nanoparticles formed at synthesis temperatures T≥500 °C, in the case of nanocomposites Ni-Co / C alloy nanoparticle formation is possible at T ≥ 270 °C, which is associated with a lower temperature com-pared to the recovery of nickel from iron. According to the results of TGA and DSC found that metals are capable of initiating the chemical transformation in the PAN, resulting in reduction start temperature degradation. Ac-cording to the results of DSC revealed that the formation of nanoparticles is accompanied by release of heat due to exothermic processes occurring in the nanocomposites. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3631

Structural features, magnetic and ferroelectric properties of SrFe10.8In1.2O19 compound

The effect of temperature on the features of the crystal and magnetic structures, as well as the magnetic properties of the solid solution of SrFe10.8In1.2O19 hexaferrite was investigated. The appearance of ferroelectric properties was detected at room temperature, which contradicts the generally accepted opinion on the description of the crystal structure of hexaferrites within the framework of the centrosymmetric P63/mmc (No. 194) space group. The reasons of spontaneous polarization in solid solutions of hexaferrites remain controversial. No deviation from the collinear magnetic structure was found in the investigated temperature range from 1.5 to 350 K, while the thermal expansion of the unit cell was practically absent in the range from 1.5 to 50 K. The crystal structure of hexaferrites was considered in the framework of both centrosymmetric P63/mmc and non-centrosymmetric P63mc space groups, which allowed us to associate the emerging spontaneous polarization with unequal distortions of neighboring oxygen polyhedra.Investigations were performed under financial support from the Russian Science Foundation (Agreement No. 19-19-00694 of 06 May 2019).Peer reviewe

The origin of the dual ferroic properties in quasi-centrosymmetrical SrFe12−xInxO19 hexaferrites

The local crystal/magnetic structures of the SrFe12−xInxO19 solid solutions (x = 0.1; 0.3; 0.6 and 1.2) were investigated using neutron powder diffraction. The measurements of the electric polarization for all investigated samples were carried out as a function of the external electric field. The presence of the ferroelectric and ferromagnetic ordering (dual ferroic ordering) in the SrFe12−xInxO19 hexaferrites at 300 K was found. This appearance contradicts to the conventional opinion describing their crystal structure (centrosymmetric space group P63/mmc (No. 194)). The reason for the existence of a spontaneous polarization (nonzero dipole moment) in the SrFe12−xInxO19 hexaferrites continues controversial. The crystal structure of the hexaferrites was considered both the centrosymmetric P63/mmc and non-centrosymmetric P63mc space groups. This fact made it possible to find a connection between the emerging dipole moment and not equal distortions of the neighbor oxygen polyhedral. The nature description of the nonzero dipole moment formation in a quasi-centrosymmetrical system of the In-substituted SrFe12−xInxO19 hexaferrites was presented based on the neutron diffraction data.This work was supported by the Russian Science Foundation (Agreement no. 19-19-00694 of 06 May 2019).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Features of structure, magnetic state and electrodynamic performance of SrFe12-xInxO19

Indium-substituted strontium hexaferrites were prepared by the conventional solid-phase reaction method. Neutron diffraction patterns were obtained at room temperature and analyzed using the Rietveld methods. A linear dependence of the unit cell parameters is found. In3+ cations are located mainly in octahedral positions of 4fVI and 12 k. The average crystallite size varies within 0.84-0.65 μm. With increasing substitution, the TC Curie temperature decreases monotonically down to ~ 520 K. ZFC and FC measurements showed a frustrated state. Upon substitution, the average and maximum sizes of ferrimagnetic clusters change in the opposite direction. The Mr remanent magnetization decreases down to ~ 20.2 emu/g at room temperature. The Ms spontaneous magnetization and the keff effective magnetocrystalline anisotropy constant are determined. With increasing substitution, the maximum of the ε/ real part of permittivity decreases in magnitude from ~ 3.3 to ~ 1.9 and shifts towards low frequencies from ~ 45.5 GHz to ~ 37.4 GHz. The maximum of the tg(α) dielectric loss tangent decreases from ~ 1.0 to ~ 0.7 and shifts towards low frequencies from ~ 40.6 GHz to ~ 37.3 GHz. The low-frequency maximum of the μ/ real part of permeability decreases from ~ 1.8 to ~ 0.9 and slightly shifts towards high frequencies up to ~ 34.7 GHz. The maximum of the tg(δ) magnetic loss tangent decreases from ~ 0.7 to ~ 0.5 and shifts slightly towards low frequencies from ~ 40.5 GHz to ~ 37.7 GHz. The discussion of microwave properties is based on the saturation magnetization, natural ferromagnetic resonance and dielectric polarization types.Investigations were performed under financial support from the Russian Science Foundation (Agreement No. 19-19-00694 of 06 May 2019).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe