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The structural and magnetic properties of YbMnO3 and Yb0.82Sr0.18MnO3 multiferroics were studied by neutron powder diffraction (NPD), magnetometry and electron spin resonance (ESR) technics in a wide temperature range. Neutron diffraction measurements showed that the substitution of ytterbium ions with strontium ions in hexagonal h - YbMnO3 (space group P63cm) leads to the destabilization of the crystal structure of the last compound and appearance of the mixture of three phases with different structure: hexagonal phase h - Yb0.95Sr0.05MnO3 (space group P63cm), orthorhombic phase o - Yb0.69Sr0.31MnO3 (space group Pbnm), hexagonal phase SrMnO3 (space group P63cm). This fact was proved by the ESR measurements in which a several signals due to the phases of different structure were observed. NPD measurements showed that the magnetic structure of h - Yb0.95Sr0.05MnO3 phase is similar to the magnetic structure of the pure h - YbMnO3 and demonstrate the presence of the antiferromagnetic ordering in the samples. ESR and magnetization measurements of h - YbMnO3 sample proved the presence of the antiferromagnetic correlations and also they showed the appearance of the ferromagnetically correlated nanoregions.

The effect of isovalent substitution of rare-earth cations on the phase separation in half-doped manganites was studied on the example of ${\mathrm{Sm}}_{0.32}{\mathrm{Pr}}_{0.18}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ by high-resolution neutron powder diffraction, neutron beam depolarization, second-harmonic magnetic response, and magnetization and resistivity measurements from 4 K up to room temperature and higher. A structural phase transition from the orthorhombic $Pbnm$ phase to a mixture of $Pbnm$ and monoclinic $P{2}_{1}/m$ phases was observed upon cooling. The magnetic ground state was found to be phase-separated into three magnetic phases emerging at different temperatures, viz., ferromagnetic (FM) and antiferromagnetic A and charge-ordered CE types. FM clusters arise far above room temperature in the orthorhombic phase and coalesce upon cooling to produce the long-range FM order below 250 K and to arrive at the percolative FM phase below 120 K. The A- and CE-type orders form in the monoclinic phase at the temperatures 200 K and 120 K, respectively. The Sm/Pr isovalent substitution qualitatively changes the phase separation and significantly increases its temperature range compared to the parent compounds. The results obtained give us knowledge of phase separation occurring in systems with strong electron correlations and extend opportunities for fine-tuning of their properties.

Here are presented investigations of powder and glass-like samples containing carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co. The neutron diffraction study reveals an amorphous structure of the samples doped with Au and Co, as well as the magnetic scattering due to a long-range FM order in the Co-doped sample. The composition and molecular structure of the sample doped with Au is clarified with the NMR investigations. The temperature dependence of the magnetization, M (T), exhibits large irreversibility in low fields of B=1–7 mT. M (B) saturates already above 2 T at high temperatures, but deviates from the saturation behavior below ~50 (150 K). Magnetic hysteresis is observed already at 300 K and exhibits a power-law temperature decay of the coercive field, Bc (T). The macroscopic behavior above is typical of an assembly of partially blocked magnetic nanoparticles. The values of the saturation magnetization, Ms, and the blocking temperature, Tb, are obtained as well. However, the hysteresis loop in the Co-doped sample differs from that in other samples, and the values of Bc and Ms are noticeably increased.

The magnetic, transport and structural properties are studied for La 0.83 Sr 0.17 MnO 3 and La 0.82 Sr 0.18 CoO 3 single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т ⁎ >T C in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator–metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn 3+ and Co 3+ ions.

Results of structural neutron diffraction study and data on the transport and magnetic properties (the linear and nonlinear (second and third order) susceptibilities) are reported for the La1-xSrxCoO3 (x = 0.18 and 0.2) polycrystals. The data on the linear and third-order susceptibilities show indications of a long - range ferromagnetic ordering with the Curie temperature (TC) about 180 K. Measurements of the second harmonic of the magnetization in the parallel ac and steady (H) magnetic fields (M2(H,T)) reveal the appearance of ferromagnetic clusters in a paramagnetic matrix below some temperature (T*) above TC. The characteristics of this clustered state and the stages of its temperature evolution are reliably determined since the non-ferromagnetic matrix affects weakly this state. It is found that a spontaneous nucleation of the ferromagnetic clusters occurs below T*, and their concentration increases sharply on cooling. Upon further decreasing temperature, the isolated clusters coalesce, leading to a percolative - type origination of a ferromagnetism. The M2(H,T) response of isolated clusters and its T-variation, including the onset of the coalescence, are very close to those found in the doped manganites, which supports an assumption on a common origin of the clustered state in these compounds.

The magnetic and structural phase diagram of perovskite manganites Sm1 − xSrxMnO3 (0.16 ≤ x ≤ 0.67) are constructed based on systematic studies by high-resolution neutron powder diffraction. It is shown that there is a clear correlation between fine specific features and temperature evolution of crystal structures and the corresponding types of low-temperature magnetic ordering. Correlations were elucidated between the crystal structure, spin ordering of the manganese ions, and the physical properties of the samariumstrontium series of manganites obtained from temperature magnetic and transport measurements.

The 152Sm0.37Sr0.63MnO3 manganite is investigated using neutron diffraction. The parameters of the crystal and magnetic structures of the manganite are determined. The diffraction data are compared with the transport and magnetic characteristics of this compound. A comparison is performed between the 152Sm0.37Sr0.63MnO3 and 152Sm0.45Sr0.55MnO3 manganites. Although these compounds differ insignificantly in the strontium doping level, are homogeneous antiferromagnets, and do not exhibit a colossal negative magnetoresistance, they have different crystal symmetries (tetragonal I4/mcm and orthorhombic Pnma), differ in the type of spin ordering (C-type antiferromagnetic and A-type antiferromagnetic ordering), are characterized by different orbital polarizations (\( d_{3z^2 - r^2 } \) and \( d_{x^2 - y^2 } \)), and possess one-and two-dimensional magnetic and transport properties, respectively. The critical concentration range in which samarium strontium manganites undergo a concentration structural transition from the orthorhombic to tetragonal crystal symmetry with a change in the type of orbital and magnetic order is revealed.

The lightly doped Nd 1− x Ca x MnO 3− δ ( x = 0.08 , 0.12; δ ⩽ 0.06 ) manganites have been investigated by means of X-ray, neutron powder diffraction, magnetization and AC magnetic susceptibility measurements. It has been shown that complex magnetic behavior of the samples observed at low temperatures can be adequately described using a magnetic phase separation model. In the framework of this model, the antiferromagnetic and ferromagnetic phases have different sign of the f–d exchange. The neodymium magnetic moments start to be ordered near the Neel temperature (Curie temperature). They are directed parallel to the moments of the manganese ions in the ferromagnetic phase, and opposite to this direction in the antiferromagnetic phase. The first-order magnetic phase transition associated with reorientation of the magnetic moments of the ferromagnetic phase along the Nd magnetic moments in the antiferromagnetic phase is observed for the samples from an intermediate range of hole concentration near T eff ∼ 9 K.

As t udy of crystal structure, elastic, and magnetic properties of low-doped Nd1−x Cax MnO3 (x 0.15) perovskites has been carried out. The ferromagnetic component is shown t oi ncrease under hole doping and, simultaneously, the temperature of the orbital order–disorder phase transition decreases. The mechanism of the concentrational transition from a weak ferromagnetic state (x = 0) to a ferromagnetic one (x > 0.15) is discussed using a two-phase model, according t ow hich the samples consist of weak ferromagnetic and ferromagnetic phase se xchange coupled at their boundary. It is found that interaction between different magnetic phases leads to spin reorientation which takes place for 0.06 x 0. 1c ompounds around Teff ∼ 9K . In the temperatur er ange from 5 to 20 K, metamagnetic behaviour is revealed for the Nd0.92Ca0.08MnO2.98 sample. H versus T as well as T versus x magnetic phase diagrams, which are characterized by the missing of a canted phase, are proposed. The appearance of orientational transitions is explained on the basis of a magnetic analogue of the Jahn–Teller effect taking into account that the magnetic moment so f Nd ions are ordered parallel to the moments of Mn ions in the ferromagnetic phase, and opposite to the direction of the weak ferromagnetic vector at T > Teff in the weak ferromagnetic phase.

Results are presented of studies of the 154Sm1−x SrxMnO3 system using neutron powder diffraction and small-angle polarized neutron scattering. An analysis of the neutron diffraction spectra showed that at T < 180 K these exhibit typical Jahn-Teller distortions of the manganese-oxygen octahedrons which persist under further cooling and on transition of the sample to a metallic magnetically ordered state. The magnetic contribution to the diffraction is satisfactorily described using the (A x (A y )F z ) model and is interpreted as the coexistence of ferromagnetic and antiferromagnetic phases. The exaggerated widths of the diffraction lines indicate an appreciable contribution from microdeformations evidently associated with the inhomogeneity of the system. Small-angle polarized neutron scattering showed that the Sm system for x = 0.4 and 0.25 is magnetically inhomogeneous in the low-temperature phase. Ferromagnetic correlations occur on scales of around 200 A and having dimensions greater than 1000 A which, combined with the temperature hysteresis of the magnetic small-angle scattering intensity observed for an x = 0.4 sample in the low-temperature phase, suggests that the transition is of a percolation nature.

The investigation of two perovskite manganites with the same carrier concentration of 0.1 electron per Mn has been performed using neutron powder diffraction and electron microscopy, and completed with transport and magnetic measurements. For ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.9}{\mathrm{MnO}}_{3},$ whatever the temperature (from 2 to 300 K), a unique crystalline structure (Pnma space group) is observed. The magnetic state below ${T}_{N}{=T}_{C}=110\mathrm{K}$ is phase separated, consisting of ferromagnetic domains of different sizes ranging from small clusters to macroscopic regions, which are embedded in an antiferromagnetic G-type matrix. The high conductivity observed in ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.9}{\mathrm{MnO}}_{3}$ at low temperature is established through a percolation of the ferromagnetic domains. At room temperature, the structure of the analogous compound ${\mathrm{Pr}}_{0.1}{\mathrm{Sr}}_{0.9}{\mathrm{MnO}}_{3}$ is cubic $(Pm3m$ space group). At low temperature $(Tl200\mathrm{K}),$ this manganite exhibits a complex microstructure, consisting of an intergrowth of G and C-type antiferromagnetically ordered layers, both from tetragonal $I4/mcm$ structure, with appreciable lattice distortion. In agreement with the insulating behavior of ${\mathrm{Pr}}_{0.1}{\mathrm{Sr}}_{0.9}{\mathrm{MnO}}_{3}$ at low temperature, no ferromagnetism is observed.

Single crystals of the isotopic `zero-matrix' samarium hexaboride (152Sm154Sm11B6) have been prepared by a modified variant of the high-temperature solution growth method. The crystals were studied by high-resolution powder (HRP) neutron diffraction and X-ray single-crystal diffractometry. The occurrence of vacancies at the boron site and complete occupancy of the metal site was established from structure refinements. The results obtained demonstrate that the use of the `zero-matrix' effect provides considerably increased precision in determining the structural parameters of atoms in hexaborides when studied by neutron diffraction.

The structural and physical properties of the electron-doped ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.9\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ perovskite manganites $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.8)$ have been studied by combining x-ray and neutron diffractions with measurements of magnetization (in static or pulsed magnetic fields), magnetic susceptibility, and resistivity. A structural change, from $Pnma$ (for $x\ensuremath{\leqslant}0.4$) to $I4∕mcm$ $(0.5\ensuremath{\leqslant}xl0.8)$, is observed at room temperature. A detailed study of two compounds ($x=0.3$ and 0.6), belonging to each structural region, demonstrates different phase separations at low temperature, with mixtures of $C$- and $G$-type antiferromagnetisms associated with different crystallographic structures ($P{2}_{1}∕m$ for $x=0.3$ and $I4∕mcm$ for $x=0.6$). The stabilization of different (crystallographic and magnetic) states together with the different N\'eel temperatures gives the opportunity to control the robustness of the antiferromagnetism versus $A$-site size parameters, such as $⟨{r}_{A}⟩$ and ${\ensuremath{\sigma}}^{2}$. Since $50\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ are not sufficient to collapse the antiferromagnetism in ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.3}{\mathrm{Sr}}_{0.6}\mathrm{Mn}{\mathrm{O}}_{3}$, a spontaneous magnetization is observed for $xl0.2$. It is demonstrated that, also in ${\mathrm{Mn}}^{+4}$-rich manganites, the magnetoresistive properties can be optimized by chemical pressure, the Sr for Ca substitution increasing the octahedra tilting in the $Pnma$ structure.

In order to investigate the paramagnetic ground state of the colossal magnetoresistance (CMR) Sm 0 . 5 5 Sr 0 . 4 5 MnO 3 compound we have used a wide set of techniques magnetoresistance, magnetization, high-resolution neutron diffraction, small-angle neutron diffraction, and muon spin relaxation. According to these measurements the paramagnetic ground state would consist of ∼0.8 nm ferromagnetic clusters embedded in a short-range charge/orbital ordered matrix. The CMR effect occurs due to percolation of these ferromagnetic clusters.

Structural neutron diffraction investigations as well as data on resistance, linear susceptibility, and second harmonic of magnetization are presented for ${}^{154}{\mathrm{Sm}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_{3}$ manganite. The structural studies reveal the unique Jahn-Teller (JT) character of this compound which is established to exhibit a $\mathrm{Pbmn}$ space group. Unusual large coherent JT distortions are found to develop below ${T}_{\mathrm{JT}}\ensuremath{\approx}180 \mathrm{K}$ and remain even in a metallic ferromagnetic phase below the Curie point ${T}_{c}\ensuremath{\approx}120 \mathrm{K}$. In the paramagnetic region the resistance is consistent with polaron hopping. A field hysteresis of the second harmonic is observed above ${T}_{c}.$ This evidences the existence of the macroscopic ferromagnetic regions in the paramagnetic matrix. In contrast, temperature dependence of the linear susceptibility reveals a plateau at $Tg{T}_{c}.$ These conflicting peculiarities of the magnetic properties can be explained by assuming the ferromagnetic behavior to be associated with the antiferromagnetic regions possessing a weak ferromagnetism. The ordered regions appear as a result of first order transition at $T\ensuremath{\approx}160 \mathrm{K},$ destroy at ${T}_{*}\ensuremath{\approx}137.5 \mathrm{K}$ and reveal a characteristic three-critical behavior for $\stackrel{\ensuremath{\rightarrow}}{T}{T}_{*}+0$. Change in a balance between the ferromagnetic double exchange hopping of ${e}_{g}$ electrons and the antiferromagnetic interactions of ${t}_{2g}$ spins, which caused by the cooperative JT effect, and the charge ordering correlations are supposed to account for the anomalous magnetic behavior above ${T}_{c}.$

We present the electronic, structural and magnetic phase diagram of the colossal magnetoresistive Sm1-xSrxMnO3 (0.16≤x≤0.67) perovskite manganites, constructed on the basis of their regular investigations by high-resolution neutron powder diffraction, temperature magnetic and transport measurements. It is shown, that a real pattern of the physical phenomena in Sm-Sr manganites is considerably more various and is interesting than it was followed from macromeasurements. The tendency of researched system to formation of the phase-separated states on crystallographic as well as, in the even greater extent, on magnetic level is demonstrated. It is shown that there is a clear correlation between fine specific features and temperature evolution of crystal structures and the corresponding types of low-temperature magnetic ordering.