Despite the 60-year history of research on band magnetism in MnSi, the field remains a vibrant area of study. This area is still of great interest although the physics of weak itinerant magnetism is complicated because of small magnetic moments and an uncertain role of local interactions. This work presents Rh-doped MnSi compounds in which a high-spin (HS) state of Mn magnetic moments has been detected in 55Mn nuclear magnetic resonance (NMR) measurements. The doping of MnSi with Rh results in a transition to the HS state for Mn1-xRhxSi at x = xc approximate to 0.025 with two Mn magnetic moments approximate to 1.3 and 2.2 mu B, which are ordered just below 200 K. This transition occurs only in part of the Mn atoms, while the other Mn atoms remain in a low-spin (LS) state. Concurrently, the Dzyaloshinsky-Moriya (DM) interaction for LS helical states of Mn moments is preserved up to x approximate to 0.13. Furthermore, variations in the Rh concentration result in discernible alterations in the magnetic field-temperature phase diagrams. In this case, it was observed that the temperature range of existence of the A phase, host skyrmion lattice, was markedly increased in presence of Rh doping, up to x = 0.025 at least. Small-angle neutron scattering has evidenced the existence of a skyrmion lattice in the helicoidal magnetic phase of Mn0.98Rh0.02Si. The Rh-doped MnSi compound thus demonstrates the coexistence of the HS and LS states of Mn. Our DFT calculations has indicated that this behavior can only be the case when Rh occupies not only Mn but also Si positions in the MnSi compound. Furthermore, our findings indicate that Ir doping of MnSi does not result in the formation of a high-temperature phase, but rather in the suppression of the DM interaction. Although Rh and Ir belong to the same column of Mendeleev's periodic table, they exhibit disparate behaviors upon MnSi doping.

Investigating the size distributions of Co nanoparticle ensembles is an important problem, which has no straightforward solution. In this work, we use the combination of 59Co internal field nuclear magnetic resonance (59Co IF NMR) and ferromagnetic resonance (FMR) spectroscopies on a metallic Co nanoparticle sample with a narrow Co nanoparticle size distribution due to encapsulation within the inner channels of carbon nanotubes. High-resolution transmission electron microscopy (TEM) images showed that the nanoparticles can be represented as prolate spheroids, with the majority of particles having an aspect ratio between 1 and 2. This observation has increased the accuracy of superparamagnetic blocking size calculations from Néel relaxation model by introducing the actual volume of the ellipsoids taken from the image processing. 59Co IF NMR and FMR experiments conducted under different temperatures allowed us to observe the thermal blocking of superparamagnetic particles in full accordance with the TEM particle volume distribution. This proved that these magnetic resonance techniques can be used jointly for characterization of Co nanoparticles in the bulk of the sample.

In the paramagnetic phase of cubic antiferromagnet SrMnO2.997 (T-N = 236 K), the spin susceptibility of the localized Mn(t(2g)) electrons exhibits a gapped behavior with d chi(s) (T) >= 0, suggesting the existence of a low-dimensional short-range magnetic order above T-N. The low-frequency fluctuations of the spin correlations of neighboring Mn4+ ions were probed by measuring the spin-lattice relaxation rate T-1(-1) and the echo-decay rate T-2(-1) of O-17 and Sr-87 nuclei up to 420 K. O-17 being involved in an Mn-O-Mn bond, the echo-decay rate T-17(2)-1 probes the fluctuations of the two neighboring S(t(2g)) spins at low frequency, omega <= 10(3) s(-1). It is shown that there exist local changes of the double-exchange interaction, which favor FM correlated pairs of neighboring S(t(2g)) spins in the Mn-O-17-Mn bond. The unusual thermal behavior of T-17(2)-1 (T) indicates low-frequency fluctuations of the short-range magnetic order which may include the change of AF <-> FM spin alignment of neighboring magnetic ions. For Sr-87 nuclei, which probe the spin configuration of eight neighboring Mn ions in the cubic unit cell, T-87(2)-1 has no such anomaly, implying that FM order should be excluded within the cubic unit cell. With both NMR probes, it is deduced that the only magnetic orders which may exist in the cubic unit cells are the following: AF-G [q = pi/a(1, 1, 1)], AF-C [q = pi/a(1, 1, 0)], and AF-A [q = pi/a(0, 0, 1)] so that the slow fluctuating short-range magnetic order is built from these three AF ordered unit cells. Furthermore, we deduce from T-17(1)-1 results that the fluctuating short-range magnetic order, i.e., corresponding to large q, has a high thermal stability in the PM phase of SrMnO2.997.

The inhomogeneous magnetic state arising from isothermal aging of the rapidly quenched U–6Nb alloy (6.3 wt % or 14 at % niobium) was studied for the first time using nuclear magnetic resonance of the 93Nb nucleus. In the process of phase transformation during isothermal annealing at Тan = 500°C, the fraction of niobium atoms in the bulk of the alloy increases in regions with a magnetic susceptibility corresponding to the alloys U1–хNbх (х > 0.14). It is shown that the process of isothermal transformation, accompanied by the formation of niobium-enriched structural precipitates, is fully completed after 60 hours.

The spin density distribution of itinerant electrons, n eg , and their effect on pairwise correlations of localized spins S ( t 2 g ) of Mn 4+ ions in cubic Sr 1 − x La x MnO 3 antiferromagnet ( x = 0.02, T N = 230 K, G type magnetic structure) is studied experimentally by nuclear magnetic resonance on 17 O nuclei. The regions with n eg > x , in which the local spin susceptibility of pairs of Mn atoms follows the dependence χ ∼ ( T − Θ) −1 with Θ = 20(5) K, indicating the growth of ferromagnetic spin correlations of neighboring magnetic ions in these domains, are found in the paramagnetic phase. The fraction of Mn-O-Mn bonds ( n eg > x ) increases with the decrease in the temperature. The interpenetrating meshes of Mn-O-Mn bonds with different densities of itinerant e g electrons form an antiferromagnetic metal phase below T N . The role of weak localization effects is discussed as the main origin of the magnetic inhomogeneity of the antiferromagnetic metal phase in Sr 0.98 La 0.02 MnO 3 .

It is shown that 139 La nuclear magnetic resonance data indicate that ferromagnetic regions are formed near La ions in cubic Sr 0.98 La 0.02 MnO 3 manganite. Part of the La ions remain in the antiferromagnetic matrix having a canted structure. The orbital and spin contributions to the shift of the 139 La nuclear magnetic resonance line, as well as the induced hyperfine fields, are determined.

It is shown that 139La nuclear magnetic resonance data indicate that ferromagnetic regions are formed near La ions in cubic Sr0.98La0.02MnO3 manganite. Part of the La ions remain in the antiferromagnetic matrix having a canted structure. The orbital and spin contributions to the shift of the 139La nuclear magnetic resonance line, as well as the induced hyperfine fields, are determined.

A comprehensive NMR study of the magnetic properties of single crystal LiCu 2 O 2 (LCO) and NaCu 2 O 2 (NCO) is carried out in the paramagnetic region of the compounds for various orientations of single crystals in an external magnetic field. The values of the electric-field gradient (EFG) tensor, as well as the dipole and transferred hyperfine magnetic fields for 63,65 Cu, 7 Li, and 23 Na nuclei are determined. The results are compared with the data obtained in previous NMR studies of the magnetically ordered state of LCO/NCO cuprates.

Comprehensive NMR investigation of low-frequency spin dynamics of LiCu2O2 (LCO) and NaCu2O2 (NCO) low-dimensional helical magnets in the paramagnetic state has been carried out for the first time. Temperature dependences of the spin–lattice relaxation rate and anisotropy on various LCO/NCO nuclei have been determined at various orientations of single crystals in an external magnetic field. The spatial asymmetry of spin fluctuations in LCO multiferroic has been discovered. The quantitative analysis of the anisotropy of spin–lattice relaxation in LCO/NCO has allowed estimating the contributions of individual neighboring Cu2+ ions to the transferred hyperfine field on Li+(Na+) ions.

Comprehensive NMR investigation of low-frequency spin dynamics of LiCu 2 O 2 (LCO) and NaCu 2 O 2 (NCO) low-dimensional helical magnets in the paramagnetic state has been carried out for the first time. Temperature dependences of the spin–lattice relaxation rate and anisotropy on various LCO/NCO nuclei have been determined at various orientations of single crystals in an external magnetic field. The spatial asymmetry of spin fluctuations in LCO multiferroic has been discovered. The quantitative analysis of the anisotropy of spin–lattice relaxation in LCO/NCO has allowed estimating the contributions of individual neighboring Cu 2+ ions to the transferred hyperfine field on Li + (Na + ) ions.

The spin density of doped electrons was investigated by Sr-87 NMR in the paramagnetic (PM) and antiferromagnetic (AF) G-type phases of electron-doped Sr1-xLaxMnO3 (x = 0.00, 0.02, 0.04; T-N = 236-200 K) ceramics with the cubic structure. It is shown that the Sr-87 NMR shift is proportional to the local density of the itinerant doped electrons surrounding the Sr sites; these electrons have mainly the e(g) character. In the PM phase, all the doped electrons are itinerant; however, they are inhomogeneously distributed in the La-containing oxides, creating electron-doped regions (EDRs) with a number of eg electrons perMn larger than in the rest of the oxide. At room temperature, the network of the overlapping EDRs does not cover all Sr sites. Nevertheless, the number of the Sr sites inside an EDR exceeds the site percolation threshold even for x = 0.02, so that the eg electrons can move on large distances. In the AF phase, below 80 K the EDRs cover the entire crystal. In this T range the doped electrons separate into two species: some of them slow down their motion and form below 50 K static FM domains, which are considered as bound magnetic polarons (MPs) of small size with the effective moment p(eff) = 23(10) mu(B) and a MP formation energy similar to 40 meV. The second species concerns the electrons which remain itinerant at low temperature participating in the fast hopping in the AF G-type ordered lattice of the Mn4+ ions. Nevertheless, their motion is slower than what is expected in an AF metal phase without cation disorder; this is probably due to the imperfect shielding of the (La3+/Sr2+) charge disorder.

The spin susceptibility of the localized Mn(t(2g)) electrons, chi(s), and the spatially distributed spin density of the doped electrons were investigated by O-17 nuclear magnetic resonance (NMR) in the paramagnetic (PM) and antiferromagnetic (AF) phases of electron-doped SrMnO3-x ceramics with the cubic structure. Three lightly doped samples (2x < 0.015) were studied with T-N = 220 K-240 K. In the PM state chi(s) increases gradually from T-N and reaches a broad maximum above similar to 1.5T(N). The gapped behavior of chi(s) indicates a low-dimensional short-range spin order persisting above T-N. These short-range one-dimensional correlations are consistent with O-17 NMR results obtained at room temperature, which show that Mn magnetic moments are aligned along the edges of the cubic unit cell. Above 350 K all doped electrons are fast-moving e(g) electrons. They provide the uniform polarization of the localized spins which increases chi(s) and the increasing doping shifts the oxygen-deficient SrMnO3-x oxide towards a ferromagnetic (FM) metallic state. At lower T the doped electrons are heterogeneously distributed in the oxide: The fraction of the fast-moving electrons diminishes and vanishes below 100 K, while the remaining doped electrons slow down their hopping and each of them creates a FM domain. These FM domains which are detected below 10 K by Mn-55 NMR can be considered as small-size magnetic polarons. Their T-activated hopping in the G-type AF lattice was probed by O-17 spin-echo experiments. The energy barrier of hopping shows a trend to grow with increasing doping, indicating that the de Gennes metallic ground state cannot be achieved in oxygen-deficient SrMnO3-x oxides, probably due to detrimental oxygen vacancy defects.

55 Mn NMR spectra in the magnetically ordered state in Sr 0.98 La 0.02 MnO 3 manganite have been obtained and the magnetic susceptibility has been measured. It has been shown that the microscopic phase separation into the antiferromagnetic matrix and ferromagnetic clusters, which can be presented as magnetic polarons, is observed in the long-range magnetic order region.

Представлен краткий обзор результатов по изучению манганитов методом ядерного магнитного резонанса (ЯМР). Рассмотрены особенности экспериментов с использованием в качестве локальных зондов ядер большинства элементов, входящих в структурные формулы исследуемых манганитов. Основное внимание уделяется применению этого локального метода для исследования микроскопического фазового расслоения по данным ЯМР 55Mn, орбитального упорядочения в LaMnO3 по данным ЯМР 17O и низкочастотной спиновой динамики.