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The effect of modulation of the decay envelope of the echo signal of 57Fe nuclei in lithium ferrite is studied experimentally, which demonstrates its intrawall origin. In contrast to cobalt characterized by a large modulating anisotropic component of the hyperfine field, which acts on nuclei in domain walls upon displacement of the latter, the manifestation of strong modulation effect in low anisotropic lithium ferrite with a relatively high mobility of domain walls is possibly caused by additional dynamic modulating effects associated with a high mobility of domain walls in this material.

ZnO photocatalytic thin films deposited on a glass substrate are obtained by chemical spraying technique, and they are active in the visible light spectrum. Optical studies have shown that ZnO thin films doped by nickel impurities absorb visible light at wavelengths from 400nm to 600nm. At the same time, this absorption rate increases with the increase of concentration of nickel impurities. At high concentration (5%), the absorption of light is reduced in the visible area, but after heat treatment at 6000C the light absorption in these samples improves, which allows us to conclude that the observed effect is caused by a violation of the homogeneity of the distribution of nickel impurities and the creation of agglomerates. Decoration of ZnO thin film surfaces by silver clusters improves light absorption, as it happens to the nanopowders, but in the case of thin films, this effect is much smaller. Experiments on methylene blue determine the significance of photocatalytic activity in the visible area of sun irradiation of ZnO thin films containing nickel impurities, which are obtained by chemical spraying technique.

In dynamic experiments using a highly sensitive torsion technique, the magnetic properties of the doped Rb3C60 single crystal are studied over a wide temperature range. The critical temperature of the superconducting transition Tc, the critical magnetic field Hc1, the pinning forces of both the Abrikosov vortices and the magnetic moments of dipoles at T >> Tc, at which relaxation processes are important, are determined and investigated. It was shown that the structural transition Fm3m-Pa3 at T = 260 K is accompanied by a reformation of the magnetic structure. Both the usual peaks at T ∼ 160–250 K and the not quite ordinary peaks of gigantic absorption of the energy of the oscillations, which shift to room temperature over time, were observed. The phenomenon is discussed in the framework of the cooperative Jahn-Teller effect, taking into account possible orbital and spin ordering. The relaxation processes at room temperatures (T ∼ 300 K) were studied. After many days of exposure (annealing) of fullerene at T ≥ 40 °C, in experiments with cooling from room temperatures, phenomena typical for a superconducting transition with giant pinning and damped oscillations were observed at T ∼ 200 K. The results of studies of magnetic phase transitions at T = 180–200 K in pure fullerite C60 (99.98% Term. Sublimed), which are related to the detected unusual magnetic phenomena in fullerene Rb3C60, are presented.

NMR spin echo at application of an additional magnetic video-pulse is a convenient method to study the domain wall pinning in magnetic materials. Domain wall pinning is the critical amplitude of the magnetic video-pulse below which the domain wall fixed. For its assessment, two alternative NMR methods were chosen. In the first case, the pinning of domain wall was measured by the action of magnetic video-pulse on a two-pulse echo signal, and in the second one, the pinning was measured at the combined action of magnetic video-pulse and radiofrequency pulses on the nuclear spin system in domain wall during the process of formation a single-pulse echo, by means of generation of the so-called magnetic echo signal.

An experimental study of the features of additional echo signal formation is described, the mechanism of which is different from the classical Hahn mechanism, in the MnxFe2-xO4 system at helium temperatures. It was found that in the MnxFe2-xO4 system, the maximum intensity of the additional echo corresponds to a ferrite having a minimum magnetocrystalline anisotropy. Exposure to a low-frequency magnetic field led to the detection of the correlation effect between the changes of the main and additional signals in manganese ferrite, at helium temperatures. This indicates that they have an intra-boundary origin, which contradicts the known interpretations of manganese ferrite NMR spectrum. The possible physical nature of the observed effect is discussed.An experimental study of the features of additional echo signal formation is described, the mechanism of which is different from the classical Hahn mechanism, in the MnxFe2-xO4 system at helium temperatures. It was found that in the MnxFe2-xO4 system, the maximum intensity of the additional echo corresponds to a ferrite having a minimum magnetocrystalline anisotropy. Exposure to a low-frequency magnetic field led to the detection of the correlation effect between the changes of the main and additional signals in manganese ferrite, at helium temperatures. This indicates that they have an intra-boundary origin, which contradicts the known interpretations of manganese ferrite NMR spectrum. The possible physical nature of the observed effect is discussed.

In this work, TiO2 micropowders and nanopowders coated by Ni nanoclusters have been prepared by original electroless deposition method. The presence of Ni nanoclusters at the surface of TiO2 grains was confirmed by measuring the temperature dependence of magnetization. Optical spectroscopy measurements showed significant increase of light absorption in Ni-coated TiO2 nanopowders. Photocatalytic properties of TiO2/Ni powder were studied with electron paramagnetic resonance spectroscopy as well. It was found that deposition of Ni nanoclusters on a mixture of anatase (76%) and rutile (14%) nanopowder provides best results and the optimal Ni deposition time was determined.

Cobalt nanowires were prepared by the electroless deposition method under an applied magnetic field. Their mixtures with copper micropowders polarized under magnetic field were compacted by a hot shock-wave method for production of oriented magnetic nanocomposites for potential rare earth free magnet applications. The magnetic properties of Co nanowire/Cu micropowder composites were studied by simple RF resonant magnetometry and Nuclear Magnetic Resonance (NMR) measurements with an optical microscopy control of obtained composite one-dimensional nanotextures.

Manufacturing W-Cu composite nanopowders was performed via joint reduction of CuO and WO3 oxides with various ratios (W:Cu = 2:1, 1:1, 1:3, 1:13.5) using combined Mg–C reducer. Combustion synthesis was used to synthesize homogeneous composite powders of W-Cu and hot explosive consolidation (HEC) technique was utilized to fabricate dense compacts from ultrafine structured W-Cu powders. Compact samples obtained from nanometer sized SHS powders demonstrated weak relation between the susceptibility and the applied magnetic field in comparison with the W and Cu containing micrometer grain size of metals. The density, microstructural uniformity and mechanical properties of SHS&HEC prepared samples were also evaluated. Internal friction (Q-1) and Young modulus (E) of fabricated composites studied for all samples indicated that the temperature 1000 °С is optimal for full annealing of microscopic defects of structure and internal stresses. Improved characteristics for Young modulus and internal friction were obtained for the W:Cu = 1:13.5 composite. According to microhardness measurement results, W-Cu nanopowders obtained by SHS method and compacted by HEC technology were characterized by enhanced (up to 85%) microhardness.

In this paper, the possibility of critical temperature increasing of superconducting precursor Tс and the current bearing capacity in samples of Bi-Pb-Sr-Ca-Cu-O superconducting system fabricated using hot shock wave consolidation (HSWC) technology and investigated by the vibrating torsional magnetometry method, was studied. The advantage of HSWC technology over the traditional technologies of superconducting composites synthesis is that the high-density materials are made from the Bi-Pb-Sr-Ca-Cu-O superconducting system. After the action of explosive wave the superconductivity is retained. After the explosion a pronounced texture is formed indicating the creation of efficient pinning centers and thus, the increase of current-carrying ability of the obtained material. The critical temperature of potential superconducting precursor Tc of transition to superconducting state increased from Tc=107K for starting sample to Tc=138K, using the HSWC technology for synthesis of samples in range of pressures from P=5GPa up to P=12GPa.

In this study, the potential possibilities of the precision of the vibrating reed method for the evaluation of the . of superconducting precursors in an HTSC Bi-Pb-Sr-Cu-O system were investigated. A special technology for obtaining these samples by using solar energy for melting and following superfast melt quenching was applied to increase their internal inhomogeneity, allowing to receive high-quality textural ceramic samples of Bi1,7Pb0,3Sr2Can-1CunOy (n=2-30) showing critical temperatures of superconducting precursor transitions above bulk Tc. To determine critical temperatures of superconducting precursors above bulk Tc for the first time, the original vibrating reed method of studying these multiphase samples in an applied magnetic field was used. It was shown that this method has sensitivity to superconducting diamagnetism making possible to reveal new superconducting precursor phases above bulk Tc.

Вивчено процеси самоорганізації магнітних полімерних карбонових нанокомпозитів, що містять нано- кластери кобальту. Встановлено, що ці процеси відбуваються завдяки дифузії магнітних наночасток, які стимулюються комбінованим ефектом зовнішніх постійних магнітних полів і нагрівання. Показано, що синтезовані полімерні композити перспективні для практичного застосування. Processes of self-assembly were studied in the magnetic polymer carbon nanocomposites doped with cobalt nanoclusters. These processes proceed due to the diffusion of magnetic nanoparticles stimulated by a combined effect of an outer steady magnetic fields and heating. The obtained polymer composites are promising for practical applications.

The effect of NMR spin-echo enhancement of 55Mn nuclei arranged in domain walls of half-metallic Heusler compounds NiMnSb and NiMnSi in the applied direct-current (dc) magnetic field was observed and studied. The effect could be associated with the increase of spin-spin relaxation time at application of the outer dc magnetic field related to the rearrangement and disappearance of the domain wall structure in the half-metallic material.

The dynamics of domain walls in magnetic cobalt microwires synthesized using electroless technology was studied by the nuclear spin echo method of 59Co nuclei located at the centers of the domain walls of the FCC cobalt phase under the influence of an additional magnetic video pulse. The measured dependences of the intensity of the echo signals on the amplitude of the magnetic video pulse allow one to estimate the pinning and mobility of the domain walls in micro- and nanowires, the anisotropy of its effect during rotation of the sample containing transversely polarized magnetic wires, and also to establish the possible type of domain walls moving in them.

The RF resonant magnetometry and NMR studies were carried out on carbon nanoparticles doped with magnetic cobalt clusters, which were synthesized by a technology combining of the hydrocarbon vapor pyrolysis and the chemical vapor deposition (CVD) process in a horizontal continuous reactor. The RF resonant magnetometry data show that the obtained carbon cobalt nanopowders are superparamagnetic at room temperatures and ferromagnetic at liquid nitrogen temperatures. The NMR study with the excitation by additional magnetic video-pulses of nanopowders obtained by using different hydrocarbons pyrolysis made it possible a fast assessment of their magnetic phase and hardness properties. The simple non-contact RF resonant magnetometry study of self-assembling processes in carbon cobalt polymer composite films synthesized using these nanopowders was made also.

The original hot shock wave assisted consolidation method combining high temperature was applied with the two-stage explosive process without any further sintering to produce superconducting materials with high density and integrity. The consolidation of MgB2 billets was performed at temperatures above the Mg melting point and up to 1000oC in partially liquid condition of Mg-2B blend powders. The influence of the type of boron (B) isotope in the composition on critical temperature and superconductive properties was evaluated. An example of a hybrid Cu-MgB2–Cu superconducting tube is demonstrated and conclusions are discussed.

Self-healing and self-organization processes were studied in the magnetic polymer nanocomposites obtained on the basis of carbon nanoparticles doped with cobalt nanoclusters, synthesized by a unique technology of chemical vapor deposition (CVD) developed by the authors. These processes proceeded with the diffusion of magnetic nanoparticles stimulated by a combined effect of outer alternative and steady magnetic fields, heating and pressure. The obtained polymer composites have good electrical and adhesion properties and are promising for practical applications.

The paper deals with the theoretical and experimental study on the multiple signals of nuclear spin echo in magnets, appearing under excitation by a periodic series of radiofrequency pulses of arbitrary duration.

We investigated the hyperthermal and magnetic properties of the stable magnetic suspension of magnetite nanoparticles. With this purpose in mind, we designed a low-frequency oscillator, 300 W, 300 KHz. A sample of the magnetic suspension was placed in the induction coil and heated up to 55°C for 30 minutes. Based on the results of measurements of transverse susceptibility, we can infer that the suspension was superparamagnetic at room temperature and transformed into the magnetic state at nitrogen temperature. Comparing the obtained experimental results with the literature data, we assessed the mean size of nanoparticles, which made up about 10 nm. Computer simulation assessment on the basis of magnetization curve gives close results.

The nature of main components of the multiple echo-response in magnetic materials upon the action of two broad resonance pulses has been revealed. It has been established that in lithium ferrite, a fast relaxing component of the multiple echo is formed by the multipulse nonresonance mechanism, whereas in cobalt, there is also a comparatively slowly relaxing contribution formed by the mechanism of distortions.

The work is devoted to the quantum-statistical investigation of echo-processes in magnets excited by a series of radio-frequency arbitrary duration pulses. The obtained theoretical results for the number of echo signals, time moments of their formation and their intensities are in good agreement with experiments carried out on magnets (ferrites, ferrometals, half-metals, manganites). The application of wide RF pulses and their sequences makes it possible to accumulate weak signals, enriches the echo-response spectrum with clearly separated intensive lines, i.e., essentially increases the sensitivity of apparatus and, correspondingly, the possibilities to explore the fine details of dynamical and relaxation processes taking place in nuclear spin-systems with sufficiently long relaxation times. The new experimental results in the study of relaxation processes are given. The high intensity of observed multiple echo signals in lithium ferrite made it possible to establish the nature of fast relaxing component in multiple-echo signal for the first time observed in FeV.

The results of the cumulative NMR stimulated echo phenomenon study in lithium ferrite are presented. This echo is generated by the joint action of a train of weak writing radio-frequency pulses and final reading radio-frequency pulse which exhibits the growth of intensity at increasing the number of exciting radio-frequency pulses. Similar effect was earlier observed for the case of cumulative stimulated photon echo.

NMR methods are successfully used in obtaining the microscopic information on the internal magnetic structure and dynamical processes in magnets. The important application of NMR in magnets is also the investigation of structure and dynamics of domain walls. In this work, it is accomplished by observation of nuclear spin echo signals of nuclei arranged in domain walls of magnets at excitation by an additional magnetic video-pulse field. We present the first systematic study of timing and spectral diagrams of magnetic video-pulse influence on the NMR two-pulse echo in a number of magnets (ferromagnets, ferrites, half metals, intermetals). It is shown that the timing diagrams showing the dependence of two-pulse echo intensity on the temporal location of a magnetic video-pulse in respect to radio-frequency pulses and spectral diagram of this influence are defined mainly by local hyperfine field anisotropy and domain walls mobility. These diagrams could be used for the identification of the nature of NMR spectra in multidomain magnetic materials and to improve the resolution capacity of the NMR method in magnets.

The character of the local electric resistance variations of film polymer composites on the basis of polyvinyl alcohol with graphite powder on the one hand and the magnetic susceptibility of the same polymer with nickel nano-particles on the other hand has been studied. It has been established that the changes of these parameters essentially depends on both initial shape of the films and on the direction of their orientation. It is concluded that the films of gradiently anisotropic polymer composites may be used in electronics. Вивчено характер зміни локального електричного опору плівки полімерних композиційних матеріалів на основі полівінілового спирту з графітовим порошком, з одного боку, та магнітної сприйнятливості того ж полімеру з нікелевими нано-частинками з іншого. Встановлено, що зміна цих параметрів істотно залежить і від первинної форми плівок, і від напрямку їх орієнтації. Показано, що плівки градієнтно анізотропних полімерних композиційних матеріалів можуть бути використані в електроніці.

Signal intensities of a two-pulse nuclear spin echo as a function of parameters of dc magnetic field pulses are measured in the series of materials: Li0.5Fe2.5–xZnxO4 (x

The competitive method of fabrication of thermo-absorbing meso- and nanosized magnetic particles was developed. Applications of high-dispersive magnetic particles could include information storage systems, biomedical fields, targeted delivery of drugs for cancer treatment, sensors, etc. By means of electroless deposition of nanoclusters on high-dispersive powder-like semiconductor TiO2 (anatase), some problems of fabrication of visible light-responsive photocatalysts are overcome or mitigated. A new method of size selection of pure TiO2 particles and micro-, meso- and nanocrystal-coated powder-like semiconductor photocatalysts with aim obtain of a uniform size distribution was developed. Catalysts Pd/γ-Al2O3, reduced in hydrogen flow, compare well with platinum catalysts by the activity in relation to breaking of bonds between carbons.

Calculations have been performed of multiple signals of nuclear spin echoes excited in ferromagnets by two radio-frequency pulses whose duration can exceed the time of free-induction decay. The values obtained for the number of echo signals and for the moments of their appearance proved to be in good agreement with the results of experiments performed using lithium ferrite.

Electroless metallization technology which allowed replacing adequately Au and Ag with Ni-P or Ni-B alloys and simplifying significantly the metallization process was developed (1-5). Other proposed patentable nanomethods for the first time allow one to produce nanochips and photomasks with nano-sized adjacent elements by single optical UV photolithography (4). The proposed nanomethods are much more advantageous and simpler than other expensive and complicated methods such as e-beam, X-ray lithography or fabrication of the nanoelements using light phase shift photomasks. The proposed methods of metallization are widely used in electronics, piezoengineering and instrument-making. As a result Au, Ag and Pd were replaced with the alloys of non-precious metals, usage of toxic substances was eliminated. Methods of fabricating the ultra-thin pore free electroless coatings on micro-, meso- and nano-sized particles are proposed.

The dependences of the intensities of two-pulse and single-pulse echoes on the time of the application of the pulses of magnetostatic field (video pulses) and on the frequency of driving pulses have been investigated experimentally. The measurements were conducted on polycrystals of metallic cobalt, half-metallic Co2 MnSi and NiMnSb, and lithium ferrite. It is shown that in lithium ferrite the single-pulse echo is formed by the stimulated mechanism of excitation, whereas in the other substances that were investigated, via the distortion of the fronts of the driving pulse. The prospects of the use of video pulses for quality control of magnetic materials is substantiated.

A simple mechanical method for the investigation of Abrikosov vortex lattice stimulated dynamics in superconductors has been used. By this method we studied the action of pulsed magnetic fields on the vortex lattice and established the resulting change of the course of relaxation processes in the vortex matter in high-temperature superconductors. This method can be used for investigation of phase transitions in vortex matter both high-temperature and exotic superconductors., Comment: 5 pages, 6 figures

Two new modulation effects are considered: the appearance of relaxation oscillations of Zeeman and dipole magnetizations in nuclear and electron paramagnets, and the manifestation of modulation in the spin-echo signals of nuclei in domain walls of magnets.

Proton spin–lattice relaxation time is determined in VH 0.68 and VH 0.73 alloys in the temperature range of β 1 , β 2 and δ ordered phases (400–100 K). Experimental results are described in terms of dipole–dipole interaction mechanism. On comparing calculated and experimental data in the complete temperature range the values of temperature dependent activation energy E a and time constant τ 0 are estimated.

The effect of NMR spin-echo enhancement of 55Mn nuclei arranged in domain walls of half metal Heusler compounds NiMnSb and NiMnSi in applied dc magnetic field was observed and studied. The effect could be related with the increase of spin-spin relaxation time at application of the outer dc magnetic field related with the rearrange and disappearance of the domain wall structure in the half metallic material.

Results of comparative study of single-pulse and two-pulse echo responses and their secondary signals in lithium ferrite speak in favor of the effectiveness of multipulse formation mechanism of the single-pulse echo and its secondary signals as well as the secondary signals of two-pulse echo. The general source for their formation is the inequilibrity of spin system at the end of a cycle of the radiofrequency pulse train in this material.

The effect of a pulse magnetic field on formation of the single-pulse echo signal in some magnetic materials has been studied. The signals of nuclear-spin echo formed by the combined action of radio frequency and magnetic pulses have been observed. The duration of the magnetic pulse was only limited by the length of the radio frequency pulse. The echo signal formed by the two magnetic pulses, the edges of a long magnetic pulse, and other situations that allowed us to reproduce the analogue of multipulse action, were observed as well.

The results of experimental study of two-pulse stimulated echo in ferromagnets of two types are presented. Ferromagnet Co and half-metal Co MnSi 2, in which a single-pulse echo formed by the distortion mechanism of the fronts of exciting pulse is also observed, are classified among the first type. Lithium ferrite and intermetal compound MnSb characterized by the absence of single-pulse echo in them - belong to the second type. For signals of two-pulse stimulated echo in the materials of the first type a short time and a long time of relaxations are observed. The short time is about the order of value shorter less than the spin-spin relaxation time. The long time is close to the transverse relaxation time of single-pulse echo formed by the distortion mechanism. The mechanisms that provide the possible interpretations of the peculiarities of the processes of nuclear magnetic relaxation are discussed., 10 pages, 7 figures

In this work the cumulative single-pulse echo effect in cobalt was studied when a train of single-pulse echoes generated by a repeating single RF pulse sequence, exhibits growth rather than damping. The phenomenon is observed below some threshold value of radio-frequency pulse power when the nonresonant mechanism of single-pulse echo excitation in cobalt becomes effective.

In the framework of the Mims transformation matrix method the equations for the nuclear magnetizations are obtained which describe the dynamics of nuclear spin-systems with strong Larmor and Rabi inhomogeneous broadenings of the NMR line in conditions of their nonequilibrium which were earlier obtained by the statistical tensors method. As an example, the properties of the proton single-pulse echo and its secondary signals in a test material (silicone oil) coated on the surface of high-Tc superconducting-oxide powders and in metallic hydride are presented.

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The results of a NMR study of the nature of main multiple nuclear spin-echo components in lithium ferrite are presented. It is shown that the strongly relaxing echo component in lithium ferrite is formed by the stimulated mechanism similar to the one observed in this material earlier for a single-pulse echo.

The results of a comparative study of domain-acoustic echo (DAE) signals in polycrystalline ferrite Co0.01Mn0.05Cu0.18Ni0.2Mg0.72Fe0.6O4, europium garnet, and iron borate are presented. The DAE signals were observed at 20MHz. They possess a long time memory and are related with displacements of domain walls. In particular, DAE in the europium garnet is characterized by particularly intensive signals and has the lowest threshold for exciting radio-frequency pulse powers and suppressing magnetic field values.