An Erratum to this paper has been published: https://doi.org/10.1134/S0031918X24120032

For the first time, an 93Nb NMR study of dichalcogenides CrxNbSe2 (x = 0.33, 0.5) in the paramagnetic state was performed. Analysis of the 93Nb NMR spectra revealed the presence in CrxNbSe2 of three magnetically nonequivalent niobium positions, whose immediate environment contains 0, 1, and 2 chromium ions, respectively. For each Nb position with a different number of chromium atoms in the immediate environment in CrxNbSe2 (x = 0.33, 0.5), the values of the components of the magnetic shift and electric field gradient tensors at the position of the niobium nuclei were determined. Evidence was obtained of the formation in Cr0.33NbSe2 of the ordering of chromium ion positions in the ab plane into a √(3) a0 × √(3) a0 superstructure. On the other hand, in Cr0.5NbSe2, no obvious indications of the formation of any superstructure of chromium ion positions were found. It has been established that the overlap of the 4d and 5s shells of niobium ions and the 3d orbitals of chromium leads to the appearance of a positive hyperfine field induced by the magnetic moments of chromium on Nb nuclei. From the temperature dependences of the shift and susceptibility in Cr0.5NbSe2, an estimate of these induced hyperfine fields is made.

The researches of the structural and magnetic properties of the layered chalcogenide Fe4Co3Se8, which has a ferrimagnetic order below T = 196 K, have been performed by means of X-ray diffraction, magnetic susceptibility measurements, and 59Co nuclear magnetic resonance (NMR) spectroscopy. It is found that the effective magnetic moment of iron ions is μeff ≈ 5.90(5) μB. The components of the magnetic shift and electric field gradient tensors at the Co nuclei sites have been determined. The hyperfine field induced on Co nuclei from neighboring iron ions has been estimated from the temperature dependences of the shift and susceptibility in Fe4Co3Se8. It was also established that cobalt ions in Fe4Co3Se8, as well as in the Co7Se8 compound, do not have intrinsic magnetic moment, but they do have a moment induced from neighboring iron ions μ _eff^Co ≈ 0.36(4) μB, which decreases at the magnetic ordering to 0.07(1)μB due to mutual compensation of contributions from neighboring iron ions.

The first principles calculations of the electronic structure and hyperfine interactions of Cr x NbSe 2 ( x = 0.33, 0.55) chalcogenides are presented. As a result, the values of the hyperfine fields and the parameters of the quadrupole interaction were determined for different arrangements of chromium ions. Ab initio calculations are compared with data obtained by the nuclear magnetic resonance methods on the 53 Cr and 93 Nb nuclei. It has been shown that Cr 3+ ions have a high degree of hybridization of a 1g and e g orbitals of 3d -electrons with 4d and 5s orbitals of niobium.It has been established that two nonequivalent environments of chromium ions coexist in Cr 0.33 NbSe 2 compound.

The structural and magnetic properties of the Co 7 Te 8 layered compound have been studied for the first time using X-ray diffraction, measurements of the magnetic susceptibility, and nuclear magnetic resonance spectroscopy on 59 Co nuclei. The nuclear magnetic resonance study of Co 7 Se 8 selenide with the same structural type (NiAs) as Co 7 Te 8 has also been performed for the first time. In contrast to Co 7 Se 8 , the ordering of vacancies and Co atoms in cation layers is absent in the Co 7 Te 8 compound, and its crystal structure is more planar and is characterized by a significantly smaller ratio c 0 / a 0 compared to Co 7 Se 8 ( a 0 and c 0 are the basic lattice parameters of NiAs). The components of the magnetic shift and electric field gradient tensors at the location of Co nuclei have been determined. A significant local charge and spin inhomogeneity of the co-mpounds has been revealed. The hyperfine coupling constant in Co ions has been estimated from the te-mperature dependences of the shift and susceptibility in Co 7 Te 8 . An anisotropic increase in the interatomic distances does not increase the localization of 3d electrons and does not lead to the appearance of magnetic moments on Co atoms in Co 7 Te 8 . This compound remains a Pauli paramagnet down to the lowest tempe-ratures.

Впервые выполнено исследование структурных и магнитных свойств слоистого соединения Co7 Te8 с помощью рентгеновской дифрактометрии, измерений магнитной восприимчивости и спектроскопии ядерного магнитного резонанса (ЯМР) на ядрах 59Co. Также впервые проведено ЯМР-исследование селенида Co7Se8, принадлежащего к тому же структурному типу (NiAs), что и Co7 Te8. В отличие от Co7 Se8 в соединении Co7 Te8 отсутствует упорядочение вакансий и атомов кобальта в катионных слоях, а кристаллическая структура Co7Te8 является более плоской и характеризуется существенно меньшим отношением параметров c0/a0 по сравнению с Co7 Se8 (a и c0 - параметры базовой элементарной ячейки NiAs). Определены значения компонент тензоров магнитного сдвига и градиента электрического поля в месте расположения ядер кобальта. Выявлена существенная локальная зарядовая и спиновая неоднородность соединений. Из температурных зависимостей сдвига и восприимчивости в Co7Te8 оценена константа сверхтонкого взаимодействия в ионах кобальта. Анизотропное увеличение межатомных расстояний не приводит к большей локализации 3d электронов и к появлению магнитных моментов на атомах кобальта в Co7 Te8. Это соединение остается паулиевским парамагнетиком вплоть до самых низких температур.

Complex sodium-containing oxides are of interest for the search and development of new materials for many practical applications. This paper presents the results of multiscale experimental and theoretical studies aimed to explore the mechanism of sodium-ion diffusion in the scheelite-related Na2Zr(MoO4)(3) and Na4Zr(MoO4)(4). These molybdates were synthesized by the precursor (formate) method. Ab initio modeling of sodium migration predicts a barrier of 1.0-1.2 eV for long-range sodium diffusion, which is confirmed by the impedance spectroscopy and the Na-23 NMR experiments. Our results allow us to assume the existence in Na4Zr(MoO4)(4) of an additional, much faster motional process (with energy barrier of 0.5-0.6 eV) associated with localized ion jumps.

The influence of the state of interfaces on the magnetoresistive properties of Co/Cu superlattices has been studied by the methods of nuclear magnetic resonance and X-ray reflectometry. It has been found that the magnetron-sputtered superlattices with the highest value of the giant magnetoresistance effect have the largest fraction of highly perfect Co/Cu interlayer boundaries, as well as practically the smallest fraction of cobalt atoms localized in the interfaces.

Research data for the diffusion mechanisms of Na+ ions in Na1 – xMg1 – xAl1 + x(XO4)3 (X = Mo, W) compounds with the NASICON-type structure (space group R $$\bar {3}$$ c, Z = 6) are reported. Solid solutions in the homogeneity range 0.1 ≤ x ≤ 0.5 for X = Mo and 0.4 ≤ x ≤ 0.6 for X = W have been prepared by solid-state synthesis. Conductivity measurements and NMR spectroscopy data indicate fast sodium diffusion in the studied samples: the ionic conductivity reaches the values of about 10–3 S/cm at T > 800 K. The frequency of elementary ionic jumps is on the order of 104 s–1 at T ≈ 500 K, and the activation energy is equal to 0.8–0.9 eV. The results have shown that the ionic conductivity in molybdates is higher than in tungstates. The growth of magnesium concentration increases the concentration of local coordinations Mg2+–Na+–Mg2+, acting as traps for moving sodium ions. The above conclusions are supported by ab initio calculations according to which the barrier for sodium diffusion from the Mg2+–Na+–Mg2+ position is expected to be higher than those for the Mg2+–Na+–Al3+ and Al3+–Na+–Al3+ ones.

We have performed Cr-53 NMR measurements on a high-purity polycrystalline sample to investigate the static and dynamic properties of a half-metallic ferromagnet CrO2. Two Cr-53 NMR lines, corresponding to magnetically nonequivalent Cr nuclei, were observed in the ferromagnetic phase of CrO2 despite all of the Cr ions being situated on the crystallographic equivalent sites. We measured the temperature dependences of the Cr-53 spin-lattice relaxation rate (T-1)(-1) in the ferromagnetic phase for the temperature range T = 4.2-360 K. It was found that in the range of low temperatures (T <= 60 K) the relaxation of nuclear magnetic moments is determined mainly by the orbital contribution proportional to the temperature, conditioned by the fluctuation of the orbital currents of d-band electrons. At temperatures T > 60 K, the main mechanism leading to the nuclear spin-lattice relaxation is a three-magnon process of scattering at which the relaxation of the nuclear spin is accompanied by the absorption of a magnon and the creation of two magnons. Based on the analysis of temperature dependences of (T-1)(-1) for two nonequivalent Cr ions, we found that their valence state is the same and corresponds to valence Cr4+, whereas the difference of resonance frequencies for these ion nuclei is conditioned by the different magnetic local fields in their location.

Spin susceptibility and low-frequency dynamics of uranium 5f electrons have been investigated by nuclear magnetic resonance (NMR) on the N-14 nuclei in paramagnetic and magnetically ordered phases for single crystalline and polycrystalline samples of uranium mononitride (UN). NMR spectra, shifts of the N-14 NMR lines, and the spin-lattice relaxation times T-1 have been obtained in the temperature range T = 10-760 K in magnetic field B = 92.8 kOe. It is shown that in the UN paramagnetic phase, temperature dependence of the N-14 NMR line shift is proportional to the spin susceptibility of the uranium 5f electrons. Joint analysis of NMR and magnetic susceptibility data allows us to determine temperature dependence of spin fluctuation energy F (T) of the uranium 5f electrons and to demonstrate that its temperature variation is close to Gamma (T ) alpha T-0.5 dependence which is characteristic of the concentrated Kondo systems above the coherent state formation temperature. In the magnetically ordered UN phase the N-14 NMR spectra consist of several lines that can be explained in terms of the model of type I antiferromagnetic order corresponding to 1k structure in the presence of magnetic domains.

The 63Cu and 27Al NMR spectra have been obtained on a polycrystalline CuAlO2 sample in external magnetic field H0 = 92.8 kOe in temperature range 30–400 K. Analysis of the 27Al NMR spectra has revealed that with temperature decrease, the NMR line shift 27K increases in magnitude and can be described by the Curie–Weiss law. Such a behavior can be attributed to the emergence of an effective magnetic moment at copper ions due to the motion of holes in the copper sublattice. In the low-temperature range, the maximum of the spin–lattice relaxation rate $$T_{1}^{{ - 1}}$$ of 27Al nuclei is observed, which is most probably induced by thermally activated diffusion of holes. Analysis of experimental data on $$T_{1}^{{ - 1}}$$ yields an estimate Ea ≈ 0.1–0.2 eV for the activation energy. The temperature dependences of the quadrupole interaction parameters indicate the crystal lattice compression along the a and c axes.

The results of investigation of the CrxNbSe2 chalcogenides (x = 0.33, 0.5) by the nuclear magnetic resonance (NMR) method on Cr-53 and Nb-93 nuclei in the magnetically ordered state at zero external magnetic field have been presented. Ab initio calculations have been performed to theoretically estimate NMR parameters and interpret the experimental data. It has been shown that the intercalation of Cr atoms into NbSe2 results in spin and charge redistributions. The lower magnetic moment of chromium nuclei, 2.2 mu(B), compared to the theoretical value mu = 3 mu(B) for Cr3+ is attributed to the high degree of hybridization of the a(1g) and e(g) orbitals of 3d Cr electrons with 4d(z2) and 5s niobium orbitals. Such a hybridization also results in the presence of a high local magnetic field in the niobium nuclei location in CrxNbSe2.

The results of investigation of the ${\mathrm{Cr}}_{x}\mathrm{Nb}{\mathrm{Se}}_{2}$ chalcogenides $(x=0.33,0.5)$ by the nuclear magnetic resonance (NMR) method on $^{53}\mathrm{Cr}$ and $^{93}\mathrm{Nb}$ nuclei in the magnetically ordered state at zero external magnetic field have been presented. Ab initio calculations have been performed to theoretically estimate NMR parameters and interpret the experimental data. It has been shown that the intercalation of Cr atoms into $\mathrm{Nb}{\mathrm{Se}}_{2}$ results in spin and charge redistributions. The lower magnetic moment of chromium nuclei, $2.2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$, compared to the theoretical value $\ensuremath{\mu}=3\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ for ${\mathrm{Cr}}^{3+}$ is attributed to the high degree of hybridization of the ${a}_{1g}$ and ${e}_{g}$ orbitals of $3d$ Cr electrons with $4{d}_{{z}^{2}}$ and $5s$ niobium orbitals. Such a hybridization also results in the presence of a high local magnetic field in the niobium nuclei location in ${\mathrm{Cr}}_{x}\mathrm{Nb}{\mathrm{Se}}_{2}$.