The nuclear quadrupole resonance study of the electron-deficient substitution in the promising thermoelectric material FeGa3 resulting in the poorly studied Fe0.92Re0.08Ga3 and Fe0.92Mn0.08Ga3 compounds has been carried out. The doping of compounds of this structure type promotes the study of the dependence of the thermoelectric characteristics on the electronic structure and finally makes it possible to increase the thermoelectric efficiency, which is very important for applications. Both compounds exhibit pronounced signatures of the formation of an additional acceptor band inside the main band gap, which is determined by rhenium and manganese substituent atoms. Nuclear quadrupole resonance spectra, as well as nuclear spin–lattice relaxation and its temperature evolution, are significantly different for the compounds under study. This difference is due to different statistical distributions of substituent atoms (predominant formation of homo- and heterogeneous dumbbells in the rhenium- and manganese-substituted compounds, respectively) caused by their outer electron shells.

The 10 % substitution of arsenic for phosphorus in FeP represents an excellent example of the preservation of the crystal and helimagnetic structure, accompanied by stabilization of the latter. Although magnetic order in FeP 0.9 As 0.1 forms at lower temperature of 90 K, it turns out to be much more resistant to an external magnetic field. Namely, no spin-reorientation transition was observed up to 12 T, as well as any other distortion of the helical magnetic structure, in contrast to the parent compound FeP.

In this work, we present the studies of structural phase transitions in FeSe 0.675 Te 0.3 S 0.025 crystals. The data obtained indicate a significant change in the behavior of many characteristics during the transition in this composition compared to the case of the unsubstituted FeSe. The resistivity at low temperatures for the studied FeSe 0.675 Te 0.3 S 0.025 is proportional to the square of the temperature, while for pure FeSe below the structural transition it depends almost linearly on temperature. 77 Se NMR studies also confirm a change in the type of phase transition. The NMR data showed a noticeable line broadening below the structural transition and an anomaly in the temperature dependence of the relaxation rate, which was not observed in FeSe. Our results confirm the quantum criticality of Fe(Se,Te) at a low Te content or existence of the nematicity change point (NCP). This makes the phase diagram of quasi-binary Fe(Se,Te) compounds generally consistent with the phase diagram of FeSe under pressure. In both cases, there is a local minimum in the superconducting critical temperature near NCP and a strong increase in the superconducting critical temperature near the point of complete suppression of nematicity.

We prepared an organically templated magnet, (enH(2))(0.5)VPO4OH (enH(2) = diprotonated ethylenediamine), hydrothermally and characterized its crystal structure by powder X-ray diffraction and Fourier-transform infrared spectroscopy, and its physical properties by magnetization, specific heat and nuclear magnetic resonance measurements and density functional theory calculations. (enH(2))(0.5)VPO4OH consists of uniform chains of V3+ (d(2), S = 1) ions and exhibits Haldane magnetism with spin gap Delta = 59.3 K from the magnetic susceptibility chi(T) at mu H-0 = 0.1 T, which is reduced to 48.4 K at mu H-0 = 9 T according to the P-31 shift. The NMR data evidence the formation of a spin-glass state of unpaired S = 1/2 spins at TS-G approximate to 3 K and indicate that the Haldane S = 1 spin chain segments are much longer in the organically templated magnet (enH(2))(0.5)VPO4OH than in the ammonium counterpart NH4VPO4OH. The single-ion anisotropy D and the interchain exchange J ' in (enH(2))(0.5)VPO4OH and NH4VPO4OH were estimated in density functional calculations to find them very weak compared to the intrachain exchange J.

In this work, we present the studies of structural phase transitions in Fe(Se,Te) crystals in the range of about 30 tellurium. We found a significant change in the properties of the ordered state of these compositions compared to the case of pure FeSe. The resistivity at low temperatures for the studied Fe(Se,Te) is proportional to the square of the temperature while for pure FeSe below the structural transition it depends almost linearly on temperature. The NMR data show a noticeable line broadening below the structural transition and an anomaly in the temperature dependence of the relaxation rate in the tellurium-substituted compounds, which was not observed in the pure FeSe. This reveals in quasi-binary compounds of iron-based superconductors a region of quantum criticality similar to that which exists when the nematicity of FeSe is suppressed under pressure and which precedes the emergence of high-temperature superconductivity in FeSe under hydrostatic pressure.

We report a detailed study of the nature of the RuGa3 in-gap states by means of precision microscopic methods: nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR), and pump-probe spectroscopy. We observe a pronounced splitting of 69Ga nuclear spin-lattice relaxation curves below-40 K and between 70 and 145 K, although the corresponding NQR lines remain narrow over the entire tem-perature range under study. The slow relaxing component behaves like a typical phonon-induced relaxation way, while the fast relaxing one demonstrates signatures of paramagnetic (below-40 K) and activation (between 70 and 145 K) mechanisms. Moreover, additional Ga' and Ga" positions with anomalously low electric field gradient were revealed for the first time for IrIn3-type structure gallides, which stay almost unchanged, at least up to 77 K. The observed microscopic features are accompanied with in-gap states saturation or depleting, which is seen as the resistivity mechanism crossover at-180 K and electron lo-calization below 145 K evidenced by pump-probe spectroscopy. Based on our experimental results, we associate this pseudo-gap like behavior with inhomogeneously distributed electronic density defects, which manifest at both micro-(nuclear spin and phonon dynamics) and macroscale (bulk transport properties such as resistivity). (c) 2022 Elsevier B.V. All rights reserved.

A comprehensive study of the intermetallic superconductor Mo8Ga41 was conducted by means of HRPXRD, abinitio calculations, NMR and NQR spectroscopy on Ga-69 and Ga-71 nuclei, as well as tunneling spectroscopy. All experimental methods used demonstrated the presence of an inherent surface superconducting phase in addition to the bulk superconducting phase. For the latter, the s-wave type single-gap superconducting behavior was observed with a slightly increased 2 Delta(0)/k(B)T(c) = 3.89 in agreement with the known enhanced electron-phonon coupling in this compound. From nuclear spin-lattice relaxation experiment, the estimated superconducting gap value of the surface phase was 2 Delta*(0) = 22.2 K, which corresponds to the T*(c) approximate to 6.3 K in the weak-coupling BCS limit. Meanwhile, the tunneling spectroscopy reveals similar values of T*(c) similar to 6.0-7.3 K for this surface phase. Thus, the known evidence of the Mo8Ga41 multi-gap behavior can be explained by the influence of the inherent surface superconducting phase.

The spatial spin modulated structure (SSMS) of the cycloid type present in bulk BiFeO3 prevents the linear magnetoelectric effect. One way to influence this structure is to reduce the crystal size to the nanoscale. Various opinions are circulating in the literature about the effect of nanocrystal size on SSMS, and to investigate this issue, we used a number of methods, with zero-field NMR (ZF NMR) spectroscopy at the forefront. ZF NMR spectroscopy enables the direct observation of the distribution profile of local fields on iron atoms and defines the SSMS presence and its properties. We also examined the synthesized samples using XRD, TEM, and magnetometry. We conclude that SSMS persists as the nanocrystal size decreases to the cycloid period and less, becoming more harmonic. This is accompanied by the change of the anisotropy type from an "easy axis" to an "easy plane". Magnetic measurements show a significant increase in the saturation magnetization, remanent magnetization, coercivity, and exchange bias of nanocrystals with sizes close to the cycloid period, which is probably associated with incomplete spin compensation in the case of an incomplete cycloid period. Despite the fact that SSMS is retained in the samples with decreased size, the magnetic properties experience a sharp increase up to applicable values.

Silver cluster compounds Ag2[B12Cl12](1), (Ag(CH3CN)4)2[B12Cl12] (2), and (Ag(CH3CN)2)2[B12Cl12] (3) with very different types of silver environment in crystals were synthesized and investigated using X-ray diffraction analysis (XRD), X-ray phase analysis and nuclear quadrupole resonance (35Cl NQR). Non-covalent interactions of chlorines with surrounding atoms were identified and analyzed using 35Cl NQR spectroscopy. The results were compared with those of XRD to show that the "short" contacts between atomic nuclei do not necessarily indicate the presence of an attraction interaction between the corresponding atoms. Numerous weak interhalogen Cl center dot center dot center dot Cl interactions were revealed in 1, while the Ag center dot center dot center dot Cl ineractions seem to be weakened due to high coordination number of silver atom. In 2, no Ag center dot center dot center dot Cl interactions were detected by X-ray diffraction, while non-covalent Cl center dot center dot center dot C, Cl center dot center dot center dot H and Cl center dot center dot center dot Cl interactions were found. As the NQR spectra indicated, interhalogen interactions in 2 appeared to be the strongest of all the others. In 3, interhalogen Cl center dot center dot center dot Cl interactions were the weakest, the largest contribution to the electric field gradient on the Cl atoms being made by silver atoms.

A detailed study of novel intermetallic superconductor Mo4Ga20Sb (Tc = 6.6 K) by means of( 69,71)Ga nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spectroscopy was performed to gain insight into the superconducting pairing mechanism and gap characteristics, as well as into the normal -state electronic properties on a microscopic scale. An unexpected step-like increase of the (69)Ga1 NQR linewidth was observed at Tc with decreasing temperature, which may indicate coexistence of several superconducting phases on a microscopic scale with slightly different T-c values. Above 140 K, the NQR linewidth decreases rapidly with increasing temperature due to possible oscillatory and/or rotational modes of the gallium cluster network at the elevated temperatures. Nuclear spin lattice relaxation rate 1/T1 of Ga-69 nuclei in the Ga1 position follows Korringa law characteristic for the compounds with good metallic conductivity. The calculated Korringa ratio S < 1 indicates the presence of antiferromagnetic correlations in Mo4Ga20Sb, in agreement with the magnetic susceptibility data. Below T-c, a pronounced intensive Hebel-Slichter peak was observed indicating s-wave superconductivity without point or line nodes in the k-space (full gap s-wave superconductivity). We have demonstrated that the best fit of the experimental data is achieved using two s-wave superconducting gaps of 13 K and 6 K with relative weights of 0.8 and 0.2, respectively. The obtained weighted average value of 11.6 K is consistent with the specific heat value of delta = 12.05 K. (C) 2022 Elsevier B.V. All rights reserved.

Various types of nanowires obtained by matrix synthesis --- homogeneous (from iron) and heterogeneous (layered) --- have been studied. A technique for obtaining arrays of layered nanowires with alternating thin layers of magnetic and non-magnetic metals (Co/Cu, Ni/Cu) has been developed and described. Microscopy methods (SEM and TEM with elemental analysis) have been used to study the topography of the resulting structures, the diameters of nanowires and the thicknesses of individual layers, and the features of interlayer interfaces. Methods of synthesis of nanowires with thin layers and clear boundaries are proposed --- dilution of the electrolyte, use of a reference electrode, control of the leaked charge. Layered nanowires have been studied by magnetometry methods and it has been shown that the magnetic properties of an array of layered nanowires (in particular, the direction of the axis of light magnetization in the Co/Cu-NP array) depend not only on the aspect ratio of the magnetic layer, but also on the ratio of the thickness of the magnetic metal layer to the thickness of a non-magnetic spacer (copper layer). The nuclear magnetic resonance (NMR) method was used to study two types of nanowires. The NMR method (on 59-Co nuclei) studied the layer structures of Co/Cu: it is shown that in nanowires with layers of smaller thickness (and, accordingly, with a large contribution of interfaces), a large proportion of Co atoms coordinated by Cu atoms is observed. The high proportion of atoms coordinated by copper suggests that an admixture of copper enters the cobalt layers. Homogeneous iron nanowires (NMR on 57-Fe nuclei) were compared with bulk iron samples. A shift of the line towards high frequencies (by 0.3 MHz) was detected, indicating an increase in the field by about 0.2 T. A significant broadening of the line and a decrease in the spin-lattice relaxation time may indicate a significant variation in the local magnetic field values. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, NMR.

In this paper, we present a protocol designed to avoid typical problems occurring in the process of the spatial spin modulated structure (SSMS) investigation in BFO-based (BiFeO3) materials by zero-field nuclear magnetic resonance (ZF NMR) spectroscopy on Fe-57 nuclei. We have analyzed the significant discrepancies in the parameters of the spectra in the literature and developed the measurement protocol to improve the quality and unify the obtained spectra. The study of the Fe-57 spectra of Sr-doped BFO at 4.2 K samples was carried out to illustrate the protocol. The obtained spectra demonstrate suppression of the SSMS by heterovalent substitution. The Sr-concentration dependent evolution of the SSMS anharmonicity parameter was observed as well.

The search for ways to realize the multiferroic potential of BiFeO3-based compounds is being relevant for three decades. The major problem is a magnetic spatial spin-modulated structure (SSMS) that nullifies the net magnetic moment over the sample volume. In this paper, we research the effect of bismuth ferrite doping with magnetic Tb3+ ions. With the help of zero-field nuclear magnetic resonance (ZF NMR) spectroscopy, we reveal a change in the type of anisotropy from "easy-axis" to "easy-plane" even at 1.5 % terbium doping. Moreover, at 8.5 % Tb doping, the magnetic structure becomes collinear, SSMS deteriorates, while the crystal structure remains rhombohedral. We also observe an additional high-frequency line, similar to the lines found in the La- and Sr-doped BFO spectra, at a frequency of 75.85 MHz. Such a combination of characteristics gives this composition every chance of being a promising multiferroic compound.

Исследованы различные типы нанопроволок, полученных методом матричного синтеза --- гомогенные (из железа) и гетерогенные (слоевые). Разработана и описана методика получения массивов слоевых нанопроволок, с чередующимися тонкими слоями магнитных и немагнитных металлов (Co/Cu, Ni/Cu). Методами микроскопии (СЭМ и ПЭМ с элементным анализом) изучена топография получаемых структур, диаметры нанопроволок и толщины отдельных слоев, особенности межслоевых интерфейсов. Предложены способы синтеза нанопроволок с тонкими слоями и четкими границами --- разбавление электролита, использование электрода сравнения, контроль протекшего заряда. Методами магнитометрии изучены слоевые нанопроволоки и показано, что магнитные свойства массива слоевых нанопроволок (в частности, направление оси легкого намагничивания в массиве Co/Cu-НП) зависят не только от аспектного отношения магнитного слоя, но и от отношения толщины слоя магнитного металла к толщине немагнитного спейсера (медной прослойки). При изучении двух типов нанопроволок применялся метод ядерный магнитный резонанс (ЯМР). Методом ЯМР (на ядрах 59Co) изучены слоевые структуры Co/Cu: показано, что в нанопроволоках со слоями меньшей толщины (и, соответственно, с большим вкладом интерфейсов) наблюдается большая доля атомов Co, координированных атомами Cu. Высокая доля атомов, координированных медью, позволяет предположить, что примесь меди входит и в кобальтовые слои. Проведено сравнение гомогенных нанопроволок из железа (ЯМР на ядрах 57Fe) с образцами объемного железа. Обнаружен сдвиг линии в сторону высоких частот (на 0.3 MHz), свидетельствующий об увеличении поля примерно на 0.2 T. Значительное уширение линии и уменьшение времени спин-решеточной релаксации может свидетельствовать о значительном разбросе величин локального магнитного поля. Ключевые слова: нанопроволоки, матричный синтез, микроскопия, элементный анализ, магнитные свойства, ЯМР.

In this paper we present study of the magnetic structure of multiferroic series Bi1-yLayFeO3 (y = 0, 0.015, 0.03, 0.05 and 0.10) using nuclear magnetic resonance (NMR) at 4.2 K and Mossbauer spectroscopy at room temperature on Fe-57 nuclei. We observed the presence of cycloid type spatial spin-modulated structure (SSMS) in the whole range of compositions. The study of the concentration dependence of the anharmonicity parameter m revealed that at the temperature of liquid helium in the composition region y = 0 - 0.10 as well as at room temperature for y = 0.03 the magnetic state of multiferroics is described by cycloid type SSMS with a positive effective uniaxial constant of magnetic anisotropy K-u > 0 ("easy axis" model). The study at room temperature in turn revealed that magnetic state of the multiferroics withy = 0 - 0.03 is described by cycloid type SSMS with a positive effective uniaxial constant of magnetic anisotropy K-u > 0 ("easy axis" model). In contrast, the magnetic state of multiferroics with y = 0.05 and 0.10 is described by a negative effective uniaxial constant of magnetic anisotropy K-u < 0 ("easy plane" model). Anharmonicity parameter m at room temperature for y = 0.03 - 0.05 is close to zero, which means that SSMS in this range of compositions is close to harmonic.

Based on a Bruker MSL-300 nuclear magnetic resonance (NMR) spectrometer, a method has been developed for upgrading the CXP, MSL, and Avance-I series spectrometers by converting them to a modern digital base and replacing analog signal processing with digital processing while preserving the standard radio-frequency (RF) components as much as possible. The upgrade means retaining the 250-W wide-band amplifier, the RF synthesizer with a frequency band of 0–250 MHz, and the narrow-band preamplifier with the complete elimination of an Aspect computer and the standard DISMSL control program. Outdated units for generating RF pulses and registering signals were modified. This enables to significantly improve the maintainability and reliability of the spectrometer and ensure its connection to a modern computer. Comparative measurements of the signal-to-noise ratio for Cu2O samples on 63Cu nuclei revealed a 1.5-fold increase in the sensitivity of the new scheme compared to the original Bruker MSL-300 NMR spectrometer.

Three salts of perchlorinated sulfonium and ammonium derivatives of tetrabuthylammonium nonachloro-closo- decaborate, (n-Bu4N)(2)[2-B10Cl9-cyclo-S(CH2)(4)S-B10Cl9] (1), (n-Bu4N)[2-B10Cl9-cyclo-S(C2H4)(2)O] (2) and (n- Bu4N)[1-B10Cl9N(n-Pr-3)] (3) are synthesized and characterized using IR, B-11, H-1, C-13 NMR, X-Ray and Cl-35 NQRspectroscopy. The noncovalent interactions involving chlorine atoms were identified by Cl-35 NQR spectra. The results were discussed in comparison with those of X-ray diffraction analysis which are based on measuring contacts shorter than the sum of van der Waals (vdW) radii of atoms. It has been found that the crystal lattice of 2 exhibits dynamic properties strongly different from those of 1 and 3. Whereas the Cl-35 NQR spectra of the latters were extremely wide (up to 1200 kHz), the spectrum of 2 demonstrated a narrowing of almost an order of magnitude (up to 120 kHz) which indicated a significant weakening of the tendency for the formation of intermolecular bonds by chlorine atoms of this cluster.