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Neutron irradiation allows the materials to transform to a state, in which the properties of material become different from an initial state. This paper presents the results of neutron irradiation of several magnetic materials including intermetallic compounds Nd2Fe14B and Er2Fe14B, multiferroics BiFe0.95Mn0.05O3 and Bi0.85La0.15FeO3, oxides LiMn2O4 and Li0.9FePO4. The fast neutrons (Eeff > 0.1 MeV) have been used in a fluence range from 1 × 1018 n/cm2 to 2 × 1020 n/cm2 at 340 K Er2Fe14B alloy becomes amorphous under irradiation, that results in the reduction of Curie temperature to about 200 K. Irradiation destroys charge ordering in LiMn2O4 leading to the transformation from an incommensurate antiferromagnetic to a commensurate ferrimagnetic structure. Neutron irradiation of BiFe0.95Mn0.05O3 oxide is accompanied by decreasing the amount of impurity phases. On the contrary, in Bi0.85La0.15FeO3 fast neutrons result in the appearance of impurity phases. Neutron irradiation distinctly affects the lattice parameters of Li0.9FePO4 compound even with the relatively low fluence.

We present susceptibility, X-ray and neutron diffraction data on powder orthophosphates LiMnPO4, LiFePO4, LiNi0.9Co0.1PO4, and LiNi0.9Mn0.1PO4. Dependences of structure parameters and magnetic state of these compounds on type of 3d element and content of 3d-electrons have been studied. Magnetic moment of 3d-transition ion is orientated along a-axis in LiMnPO4, along b-axis in LiFePO4, and along c-axis in both LiNi0.9Mn0.1PO4 and LiNi0.9Co0.1PO4. At low temperatures, a magnetic moment magnitude is equal to 4.0 μB in LiMnPO4 and LiFePO4 samples, while it is twice less for LiNi0.9Co0.1PO4.

Experimental studies of the influence of fuel burnup in the range (3.1–6.9)·1021 fissions/cm3 and subsequent isochronous thermal annealing in the range 150–580°C in 1 h on the change in the structure and structural parameters of the components of dispersion fuel (U–Mo)/Al irradiated in IVV-2M are presented. It is found that the changes in the lattice parameters of the alloy γ-(U–Mo) and aluminum with increasing burnup and annealing temperature are of multistage character. It is determined that as fuel burnup increases the change in the lattice parameters of the alloy and aluminum is nonmonotonic, while the lattice parameters decrease monotonically with increasing temperature of isochronous annealing.

The original version of the exchange-striction model of a ferrimagnet has been employed for calculating a number of magnetic properties of RCo2 ferrimagnets, where R = Er, Ho, Dy, Tb, and Gd are rareearth ions. The following magnetic properties are calculated: pressure dependence of the Curie temperature (Т С), temperature dependences of magnetization in sublattices of cobalt and rare-earth atoms, and isotherms of magnetization of these lattices at Т > Т С. For an ErСо2 sample, the Н–Т phase diagram has been constructed and the magnetization in the magnetic fields Н = 0–70 Т has been calculated. The calculated and experimental results have been compared. Based on the exchange-striction model, the qualitative explanation of the difference in the type of the magnetic phase transformation in the intermetallic compounds with R = Tb and Gd and R = Er, Ho, and Dy is given.

Results are given of measurements of X-ray and neutron diffraction, small-angle neutron scattering, and field dependences of the magnetization for nanocomposites formed by multilayer graphene and iron particles. Four samples have been investigated that differed in the content of Fe as follows: 0.75, 30, 45, and 70 wt %. The calculations of the X-ray diffraction and neutron diffraction patterns show that the size of graphene particles is about 4 nm, and the size of the iron domains of coherent scattering is no less than 50 nm. The content of the Fe particles in the composites has been estimated based on the data of the measurements of neutron diffraction, small-angle neutron scattering, and magnetization. The values of the iron concentration obtained by different methods differ quite significantly. The difference is caused by the specific character of the methods of measurements.

We present the susceptibility and neutron diffraction data on multiferroic Ni 3− x Co x V 2 O 8 with x =0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order–disorder transition occurs at T HTI =8.5 K in both samples. Below T HTI , the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x =0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x =0.5 exhibits a definite temperature dependence, which differs from the case of the undoped sample ( x =0).

The temperature dependence of the magnetic moments of cobalt and holmium ions in the temperature range of 5–300 K at pressures of P = 0 and 5 kbar was determined based on neutron diffraction data on Ho(Co0.9Ga0.1)2 intermetallide. The temperature dependence of the lattice parameter was established, and the spontaneous bulk magnetostriction was determined. These quantities were calculated using the exchange striction model of a ferrimagnet, and good agreement with the experiment was obtained. The parameters of the exchange interaction between pairs of atoms of this compound and the magnetoelastic coupling constant were estimated. An original interpretation of the nature of the first-order magnetic phase transition in HoCo2 is proposed.

Multiferroic composites of (x)NiFe2O4 + (1-x)BaTiO3 with x = 0.2, 0.3 and 0.4 and (x)CoFe2O4 + (1-x)BaTiO3 with x = 0.2, and 0.4 have been synthesized by mixing NiFe2O4 (CoFe2O4) spinel and BaTiO3 piezoelectric. Distribution of Ni (Co) ions on 8a and 16d positions of spinel lattice (space group Fd-3m) is determined by neutron powder diffraction. Wave vector of magnetic structure of the spinel is k = 0. The dielectric permittivity of the composites was measured for the frequency range 102 – 105 Hz. At low frequencies the dielectric permittivity decreased from ~940 for x = 0.2 to ~360 for 0.4.

To study the evolution of structural and magnetic states of irradiation-amorphized Er2Fe13.8B alloy during isothermal annealing at temperatures of 295–1025 K, magnetization measurements and neutron diffraction analysis have been performed. The annealing of the alloy leads to the crystallization of the Nd2Fe14B-type phase, the amount of which reaches about 84% of the sample volume, and α Fe (16%). Neutron diffraction studies have shown that the Er2Fe13.8B alloy crystallizes in a temperature range of 590–638 K. Magnetic measurements indicate the increase in the spontaneous magnetization and coercive force as the annealing temperature increases above 800 K. The magnetization of the Er sublattice in the sample annealed at 993 K is lower than that of the crystalline sample before its amorphization. However, the magnetic anisotropy of the Er sublattice is unchanged, i.e., the easy axes remain oriented in the basal plane of the tetragonal lattice.

This paper presents the results of investigations of the structural state and magnetic properties of nanocrystalline cupric oxide samples with average particle sizes of approximately 40 and 13 nm, which were synthesized by the electric explosion and gas phase methods, respectively. The samples have been studied using X-ray diffraction, neutron diffraction, magnetic measurements, high-resolution transmission electron microscopy, and copper nuclear magnetic resonance. It has been shown that, in the initial state, regardless of the synthesis method, CuO nanoparticles are characterized by a heterogeneous magnetic state, i.e., by the existence of long-range antiferromagnetic order, spontaneous magnetization, especially at low temperatures, and paramagnetic centers in the material. The ferromagnetic contribution is probably caused by the formation of magnetic polaron states due to the phase separation induced in the system by excess charge carriers as a result of the existence of point defects (vacancies in the anion sublattice) in the nanocrystalline state. In this state, there is an inhomogeneously broadened nuclear magnetic resonance spectrum, which is a superposition of the spectrum of the initial antiferromagnetic matrix and the spectrum of ferromagnetically ordered regions. At high concentrations of ferromagnetically ordered regions, the antiferromagnetic matrix exhibits a nuclear magnetic resonance spectrum of CuO nanoparticles, predominantly from regions with the ferromagnetic phase. The appearance of magnetization can also be partly due to the frustration of spins in CuO, and this state is presumably localized near the most imperfect surface of the nanoparticles. The magnetic susceptibility of nanoparticles in the initial state in strong magnetic fields is significantly higher than that for the annealed samples, which, most likely, is associated with the influence of the high concentration of magnetic polarons. No correlation between the ferromagnetic contribution and the size of particles is found. In the CuO samples annealed at 400°C in air, when the average size of CuO nanoparticles remains unchanged, the ferromagnetic contribution completely disappears, and the magnetic behavior of the nanoparticles becomes qualitatively similar to the magnetic behavior of bulk CuO.

Magnetization and neutron diffraction measurements have been carried out to study evolution of structure and magnetic states of amorphous Nd 2 Fe 14 B and Er 2 Fe 14 B alloys under isothermal annealing at 295–1025 K. The amorphization have been performed by neutron irradiation which provides a homogeneous state in different with other methods of amorphization. The annealing induces a rise of α-Fe phase content in alloys and a recrystallization into Nd 2 Fe 14 B-type phase. Neutron diffraction data show that the recrystallization occurs over narrow temperature interval (590–638) K in Er 2 Fe 14 B and at around 800 K in Nd 2 Fe 14 B. Magnetic measurements testify that in both samples the magnetization and coercive field increase with annealing temperature above 800 K.

The results of the comparative analysis of the Ti 50Ni 25Cu 25-alloy structures produced in the initial amorphous state by rapid quenching from the melt (RQM), after severe plastic deformation by torsion under high pressure (HPT), and postdeformation heat treatment (PHT) are presented. The study was carried out using neutron and X-ray diffraction, transmission and scanning electron microscopy, and measurements of electrical properties. The initially amorphous alloy has been established to nanocrystallize after torsion under a pressure of 7 GPa to 0.5 revolutions of the anvil. Then, after 1, 5, 10, and 15 rev, the alloy again undergoes the strain-induced amorphization even with the retention, even after 5-15 rev, of a large number of highly dispersed nanocrystals less than 3-4 nm in size with a distorted B2 lattice in the amorphous matrix. Their crucial role as nuclei of crystallization provides the total low-temperature nanocrystallization during subsequent annealing starting from 250-300°C. It is shown that PHT of the alloy amorphized by HPT makes it possible to produce extremely uniform nanocrystalline (NC), submicrocrystalline (SMC), or bimodal (NC + SMC) austenitic B2-type structures in it. A complete diagram of thermoelastic martensitic transformations in the region of B2-austenite states, from nanostructured state to conventional polycrystalline one, has been constructed. The size effect on the stabilization of martensitic transformation in nanocrystalline B2 alloy has been established. © Pleiades Publishing, Ltd., 2012.

Solid solutions of the ZrO2-CaO system with 7, 9.6, and 20 mol % of calcium oxide are analyzed by X-ray and neutron diffraction and small-angle neutron scattering. Samples are synthesized by the sol-gel method and annealed at the temperature T = 600°C for 4 h. All samples have a tetragonal structure (P42/nmc space group). The size of crystallites is 10–20 nm. Small-angle neutron scattering curves are characterized by a peak near the momentum transfer q = 0.5 nm−1. The existence of the peak is caused by correlation between solid nanoparticles in the samples. Density correlation functions are numerically computed from the experimental small-angle scattering cross-sections by the inverse Fourier transform. Correlation lengths, concentrations of scattering nanoparticles, and specific surface areas of the samples are determined.

Ferrogarnets of the system {Y3}[Fe2-xScx](Fe3)O12 were investigated by neutron diffraction and magnetic methods. Parameters of crystal structure were refined. It was found that deviations from a collinear ferrimagnetic structure emerged at x ~ 0.7. At high concentrations of Sc a growth of the high-field magnetic susceptibility and an abnormal temperature dependences of dynamic susceptibility typical of local angular spin structures were revealed. The fracture temperatures for the local angular structures were determined.

Six samples of Nd-Fe-B-permanent magnets, distinguished in the texture degree, have been measured by neutron diffraction in the reflection and transmission regimes. The texture in the samples was formed by application of impulses of external magnetic field 0H = 4 T. Analysis of the obtained neutron diagrams by means of the Fullprof program allowed quantitative determination of the texture degree and conclusion to be made that the texture degree grows with an increase in numbers of magnetic field impulses.

The specific features of the crystal structure and the magnetic state of stoichiometric lithium manganite in the structurally ordered Li[Mn2]O4 and disordered Li1 − δMnδ[Mn2 − δLiδ]O4 (δ = 1/6) states have been investigated using neutron diffraction, X-ray diffraction, and magnetic methods. The structurally disordered state of the manganite was achieved under irradiation by fast neutrons (E eff ≥ 1 MeV) with a fluence of 2 × 1020 cm−2 at a temperature of 340 K. It has been demonstrated that, in the initial sample, the charge ordering of manganese ions of different valences arises at room temperature, which is accompanied by orthorhombic distortions of the cubic spinel structure, and the long-range antiferromagnetic order with the wave vector k = 2π/c(0, 0, 0.44) is observed at low temperatures. It has been established that the structural disordering leads to radical changes in the structural and magnetic states of the LiMn2O4 manganite. The charge ordering is destroyed, and the structure retains the cubic symmetry even at a temperature of 5 K. The antiferromagnetic type of ordering transforms into ferrimagnetic ordering with local spin deviations in the octahedral sublattice due to the appearance of intersublattice exchange interactions.

The structures and magnetic states of stoichiometric lithium manganite LiMn2O4 and manganites and titanates Li1.33Mn1.67O4 and Li1.33Ti1.67O4 with excess lithium in both the initial (as-synthesized) state and after irradiation by fast (Eeff ≥ 1 MeV) neutrons with a fluence of 2 × 1020 cm−2 have been studied using neutron diffraction, X-ray diffraction, and magnetic methods. It has been established that the irradiation brings about a noticeable redistribution of manganese, titanium, and lithium cations over nonequivalent tetrahedral (8a) and octahedral (16d) positions of a spinel lattice. This structural disorder causes a radical change in the physical properties of the materials under study. The charge order existing in the initial LiMn2O4 sample is destroyed. There arises a strong intersublattice indirect exchange interaction Mn(8a)-O-Mn(16d). The disorder is accompanied by the antiferromagnet-ferrimagnet (LiMn2O4) and paramagnet-ferrimagnet (Li1.33Mn1.67O4) magnetic transitions.

The magnetic structure of intermetallic compounds Ce2Fe17 − xMnx (0 ≤ x ≤ 3) was studied using neutron diffraction. The neutron diffraction patterns measured at 4.2 K contain satellites indicating a modulated structure with the wave vector k = [0, 0, τ]. As the concentration x increases, the value of τ increases, while the average magnetic moment of Fe/Mn atoms decreases. A change in the magnitudes of the average magnetic moment and wave vector k is explained by competition between exchange interactions at distances of nearest neighbor transition element atoms.

Magnetic and neutron-diffraction methods have been used to study the magnetic state of polycrys- talline and amorphous samples of the intermetallic compound Ce 2 Fe 17 . The amorphous state was obtained by irradiating the intermetallic compound by fast neutrons. It has been shown that the competition of ferromag- netic and antiferromagnetic interactions between the nearest-neighbor iron atoms, which is responsible for the formation of the magnetic state, manifests itself differently in the crystalline and amorphous states. In the crys- talline sample, an increase in temperature leads to a transition of a collinear ferromagnet into an antiferromag- net. In the amorphous intermetallic compound, the competition leads to local spin deviations, which cause the appearance of some low-temperature features in its magnetic properties. Based on experimental data, H - T mag- netic phase diagrams of the crystalline and amorphous Ce 2 Fe 17 have been constructed. It has been shown that the magnetic field destroys both the antiferromagnetic state in the crystalline Ce 2 Fe 17 and the low-temperature mixed (combining properties of ferromagnets and spin glasses) magnetic state in the amorphous Ce 2 Fe 17 .

The Tb0.1Tm0.9Co2 compound is investigated using neutron diffraction. It is shown that this compound undergoes an irreversible band metamagnetic transition induced by an external magnetic field. The magnetization of the Co sublattice increases from 0.2 to 0.6 μB. The critical field strength is approximately equal to 1 T at temperatures of 1.8 and 4.0 K. As the temperature increases, the effect of the magnetic field on the magnetic state of the sample weakens and, at 25 K, no noticeable changes are observed in an external field of 0.75 T. The metamagnetic transition at 1.8 K is accompanied by the disappearance of rhombohedral distortions and brings about a lattice expansion by approximately 1%.

Neutron and X-ray diffraction have been used to study the structural state of polycrystalline samples of the perovskite-like manganite La0.825Ba0.175MnO3 with different concentrations of antisite defects produced by fast-neutron irradiation. It has been established that the concentration of antisite defects depends linearly on the fraction of the sample volume affected by cascades of atom-atom displacements, reaching at high fluences a value equal to 0.0875, which is “limiting” for a given composition. The formation of antisite defects is accompanied by the appearance of significant static uncorrelated ion displacements, which for oxygen ions become greater than their tilting displacements. It has been shown that in this case, the tilting mode ϕ, which forms the rhombohedral structure of the manganite, is not destructed completely, although the magnitude of correlated tilting displacements decreases noticeably.

The electric resistivity and neutron diffraction measurements of the intermetallic compounds Nd{sub 1-x}Tb{sub x}Co{sub 2} (x = 0, 0.2, 0.3, 0.5, 0.7, or 1) have been performed. All compounds have a cubic structure at room temperature and a rhombohedral structure at 4.2 K. The magnetic structure of these compounds is described by the wave vector k = 0. The magnetizations of the rare earth and cobalt sublattices increase with increasing x. The concentration dependence of the cobalt sublattice magnetization is explained on the basis of the model of metamagnetic band subsystem in compounds of the RCo{sub 2} type.

The structural state of nanocrystalline samples of expanded graphite is investigated using X-ray diffraction and neutron diffraction analyses. The expanded graphite samples are prepared by a rapid thermal decomposition of intercalation compounds of oxidized graphite based on fluorinated graphite, graphite oxide, and graphite aminofluoride. It is established that the main phase of expanded graphite belongs to the hexagonal crystal system (space group P63/mmc) and that carbon atoms in the structure occupy the 2b and 2c positions. The unit cell parameters and the unit cell volume in the structure of expanded graphite samples are larger than those in the structure of massive graphite.

The structural and magnetic states of LaMnO 3 samples containing various concentrations of antisite defects created by fast-neutron irradiation were studied by neutron diffraction, x-ray diffraction, and magnetic measurements. It is found that the static uncorrelated displacements of oxygen ions induced by the formation of antisite defects break the Jahn-Teller Q 2 mode and the initial orthorhombic O '-type structure transforms into the pseudocubic O * modification. As a result, the indirect ferromagnetic exchange caused by the overlap of the e g orbitals of manganese ions and the p σ orbitals of oxygen ions becomes three-dimensional and the initial A - type antiferromagnetic phase transforms into a canted ferromagnetic phase. The magnetic phase diagram of LaMnO 3 is plotted for various defect concentrations.

The magnetic structures of the intermetallic compound La0.75Sm0.25Mn2Si2 were determined over the temperature region 4.2–500 K by magnetic methods and neutron diffraction. Four different magnetically ordered states are found with critical temperatures of the magnetic phase transitions at TSm=14 K, TAF=150 K, TC=305 K, and TN≈500 K. The peculiarities and possible reasons for the existence of these phase transitions are discussed.

Neutron powder diffraction was employed to study for the first time the pressure effect on the magnetic transition in the pseudo-binary Laves-phase compound Ho(Co0.9Ga0.1)2 and to determine the magnetic moments of the Ho- and Co-subsystems. The pressure effect on TC is found to be negative and extremely large, namely ∂T C /∂p∼−3.4 K/kbar . The values of the magnetic moments of the Ho and Co ions are found to be μHo∼9.7μB/atom, μCo∼1.2μB/atom at p=0 and μHo∼9.3μB/atom, μCo∼0.7μB/atom at 5 kbar.

The crystal structure and magnetic state of the compounds Ce 2 Fe17, with Curie temperature T C ranging from 20 to 116 K, but almost constant Neel temperatures T N ≈ 206 K, were studied by X-ray and neutron–diffraction methods and magnetic measurements. The relation between the magnetic state and the real crystal structure of Ce 2 Fe 17 is discussed.

The peculiarities of oxide phase formation processes under the pyrolysis of salt and polymer–salt compounds based on polyvinyl alcohol and molybdenum and tungsten salts acidified by nitric acid have been studied. For that samples were prepared by annealing in a temperature range of 100–600°C and investigated by small-angle neutron scattering and X-ray diffraction methods. Similar samples with no polymer in their composition were studied for comparison. A size distribution of oxide phase particles, a specific surface area, a volume fraction and a mean particle size were found to be dependent on an annealing temperature and availability of the polymer. The characteristics of the above samples were compared with those of the earlier samples synthesized from solutions with a naturally established acidity. A mechanism of oxide particle formation under a thermal decomposition of the acidic compounds is provided.

Nanocrystalline manganites Lae.eAgs.1MnO3, La6.7Ags.3MnO3, and Lao.TSre.rMnOr have been synthesized by pyrolysis and subjected to isothermal annealing. The atomic, magnetic, and mesoscopic structures of these manganites were investigated using magnetic measurements as well as X-ray and neutron diflraction. Particles of sizes ranging from 3G40 to 600-700nm coalesced with an increase in the annealing temperature from 600'C to 1300"C. All investigated samples had a rhombohedral structure and were ferromagnetic. The Curie temperature o( the samples containing silver decreased while that of the samples containing strontium increased with the annealing temperature (i.e. with the growth in particle size). The magnetization of the Mn ions increased with annealing in all three systems. It is reasonable to assume that the growing size o( the nanoparticles lead to an increased magnetization owing to the reduction of the angie between the nearest magnetic moments ol the Mn ions. e 2004 Elsevier B.V. All rishts reserved.

Neutron diffraction patterns of three argon hydrates which exist at the pressures up to 10 kbar has been studied; Rietveld refinement of their structures has been done. The phase which is stable from 1 bar to 4.6 kbar appears to be typical cubic structure II gas hydrate with variable degree of filling of the large cavities. Stoichiometry of this compound under high-pressure conditions has been determined for the first time and appears to be ArW4.5H2O and Ar·4H2O at 3.4 and 4.3 kbar, respectively. Gas hydrate existing in the pressure range of 4.6–7.7 kbar has a hexagonal structure (hexagonal structure III, so-called structure H). Refinement of the structure has shown that the best agreement between calculated and experimental pattern can be reached in the case of accommodation of five (!) argon atoms in the large cavity. Indexing of the neutron diffraction pattern of the hydrate stable in the 7.7–9.5 kbar range leads to the primitive tetragonal unit cell with parameters a = 6.342 A, c = 10.610 A at 9.2 kbar, which does not correspond to any known type of gas hydrates. The water framework of this structure was found by idealizing the structure of pinacol semiclathrate hydrate. This hydrate belongs to a new, earlier unknown, tetragonal structural type of gas hydrates. It contains only one type of polyhedral cavities with 14 faces. This type of polyhedrons are space-filling; two argon atoms occupy each cavity. This structure gives the first example of the gas hydrate water framework which contains only one type of polyhedral cavities.

Nanocrystalline samples of the manganites La0.9Ag0.1MnO3, La0.7Ag0.3MnO3, and La0.7Sr0.3MnO3 were synthesized through pyrolysis and isothermally annealed. The atomic, subatomic, and magnetic structures of these manganites were studied using magnetic, x-ray, and neutron diffraction measurements. Increasing the annealing temperature from 600 to 1200°C coarsens the grains from 30–40 to 600–700 nm in size. All the samples studied have rhombohedral structure and are ferromagnets. The Curie temperature decreases for the samples doped by silver and increases for the samples doped by strontium as the anneal temperature is increased. The magnetization of the Mn ions increases with nanoparticle size in all the three systems, which indicates the presence of a size effect.

We have investigated the magnetic structure of TbNi5 using neutron diffraction from 2.2 to 30 K to find new magnetic satellites below TC = 23 K, which have never been reported before. These satellites can be indexed as (0,0,1±τ), (1,0,1±τ), (0,0,2±τ), and (1,0,2±τ), where τ is equal to 0.0194 r.l.u. (reciprocal lattice units). We have observed these new peaks in addition to magnetic peaks seen in previous measurements. We can understand this long-period incommensurate structure in terms of two propagation vectors: k1 = (0,0,0) and k2 = (0,0,τ). From the temperature dependence of the intensity of the commensurate and incommensurate peaks as well as our heat capacity data, we suggest that TbNi5 should have a modulated magnetic structure over the whole temperature range from 23 to 2 K, in contradiction to the long held view that TbNi5 is a collinear ferromagnet below TC = 23 K.

The influence of hydrostatic pressure (up to 5 kbar) on the magnetic structure of Ce2Fe17 was investigated using neutron diffraction in the temperature range from 2 to 300 K. The existence of a collinear ferromagnetic phase below 95 K with a magnetic moment of Fe, mFe=2.0 μB, was confirmed at ambient pressure. Magnetic peaks present between 95 and 205 K correspond to an incommensurate antiferromagnetic structure with a wave vector changing its value from τ1=0.026 A−1 at 100 K to τ1=0.034 A−1 at 205 K. A helical model is used to describe the magnetic structure. Application of high pressures leads to significant changes of the magnetic structure. The ferromagnetic phase, suppressed in the studied temperature range by pressures higher than 3 kbar, gets substituted by a new incommensurate antiferromagnetic phase. This phase can be described as a superposition of the helical structure with a second antiferromagnetic coupling with propagation vector τ2≈0.078 A−1 at 40 K under pressures above 3 kbar. The correla...

Neutron diffraction measurements of the Nd5Ge3 intermetallic compound with a hexagonal structure (space group P6(3)/mcm) have been performed at temperatures of similar to 10 and 293 K. The basis functions of irreducible representations of the space group D (6h) (3) (P6(3)/mcm), which are calculated as a result of the symmetry analysis of possible magnetic structures with the wave vector k = mu b (1), are used to facilitate the search for a real model of the magnetic structure of the compound.

The compounds Ce 2 Fe 17− x Mn x ( x =0–3) were synthesized and their structure and magnetic properties were studied. The compounds crystallize in the rhombohedral Th 2 Zn 17 -type structure. Neutron diffraction study of Ce 2 Fe 17− x Mn x solid solutions shows that Mn prefers the 6 c site and avoids completely the 9 d site, whereas the 18 f and 18 h sites are occupied almost randomly. The compositional dependences of the unit cell parameters at 293 K are non-monotonous. The binary compound Ce 2 Fe 17 shows ferromagnetic behavior below Θ=94 K and helicoidal antiferromagnetic structure with T N =206 K. The Neel temperature of the compounds Ce 2 Fe 17− x Mn x decreases almost monotonously with increasing Mn content, whereas Θ( x ) dependence is non-monotonous. Ferromagnetic order disappears in the range x =0.5–1. Probably, the compounds with 1 x ≤2 at low temperatures are inhomogenous ferromagnets consisting of microscopical regions with ferromagnetic ordering. Simultaneously, a short-range helicoidal antiferromagnetic state exists in the latter compounds. A magnetic phase ( x − T ) diagram is presented. The magnetization curves of the compounds with x =0.5–1 show a metamagnetic transition at ∼(4–7) kOe.

The crystal structure and the magnetic state of polycrystalline LaMn 1 - x V x O 3 (0.1 0.8; at this transition occurs through an intermediate state exhibiting spin-glass properties. © 2000 MAIK "Nauka/Interperiodica".

The structural changes in the high temperature superconductors (HTSC) samples of the compounds YBa2Cu3O6·95 and La1·83Sr0·17CuO4 under pressure being unirradiated and irradiated by fast neutrons have been studied by the neutron diffraction method. The different anisotropy of crystal lattice compression was found for these compounds in the initial and irradiated states.

The pressure dependence of the crystal structure of a powder sample of Y2Fe15·3Si1·7 was studied in the pressure range from 0 to 2 GPa, using the D-2 diffractometer with hydrostatic liquid pressure cell at the IVV-2M reactor (Ekaterinburg) and DN-12 time-of-flight diffractometer with a sapphire anvil cell at the IBR-2 pulsed reactor (Dubna). Also the pressure dependence of the Curie temperature Tc (P) of the alloy was studied. The correlation between the decreases of both Tc and Fe-Fe interatomic distances in “dumbbell” site 4f under pressure was obtained.

The elastic neutron scattering in polycrystalline samples of the (Ni 1 - x Li x )O solid solutions ( x < 0.1) is investigated by neutron diffraction technique. It is shown for the first time that the doping of nickel monoxide by lithium is accompanied by the formation of vacancies in the anionic sublattice, and the vacancy concentra- tion is equal to the lithium content in the solid solution. The neutral lithium atoms are randomly arranged over sites of the cationic sublattice with possible spatial polarization of a valence electron toward an oxygen vacancy. In the composition range studied, the diamagnetic dilution of nickel monoxide by lithium turns out to be mag- netically similar to the dilution with magnesium. In both cases, the Neel temperature and the mean magnetic moment per atom linearly decrease with an increase in concentration of the diamagnetic dopant. © 2000 MAIK "Nauka/Interperiodica".

Magnetic neutron diffractometry revealed the existence in (Fe1−xCox)Ge2 solid solutions (x

The methods of neutron diffraction, X-ray and magnetic measurements were used to study the structural and magnetic states of disordered samples of manganite La0.825Ba0.175MnO3. A disordered state was attained by irradiation with fast neutrons. It was established that the ferromagnet spin glass-like magnetic transformation takes place at a substitution concentration of ∼6%. A magnetic state diagram of structurally disordered manganite was constructed. The magnetic state transformations are explained by the effect of localization of eg-electrons responsible for kinetic ferromagnetic exchange. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tm(Co1−xAlx)2 compounds with x=0; 0.05; 0.10 and Tm(Co0.95Si0.05)2 have been studied by means of ac-susceptibility, magnetization, magnetostriction, electrical resistivity and neutron diffraction measurements. It is shown that the magnetic state of TmCo2 is characterized by the absence of the Co-magnetic moment and by the presence of the localized spin density fluctuations in the d-subsystem at low temperatures and is strongly affected by an applied magnetic field. The partial substitution of Al or Si for Co in TmCo2 leads to the appearance of the long range magnetic order and gives rise to the Co-magnetic moment up to MCo=1.25 μB. In Tm(Co0.9Al0.1)2, the field-induced phase transition in d-subsystem was observed at the critical field Bc≈17 T using high-field magnetization and magnetostriction measurements. This phase transition is associated with a collapse of the Co-magnetic moment. Instability of the Co-magnetic moment in TmCo2 at the substitution and in an applied magnetic field is explained by the closeness of the molecular field acting on the Co-subsystem to the critical value of the Co metamagnetic transition field.

Using the methods of neutron and X-ray diffraction analysis and magnetic measurements, polycrystalline samples of LaMnO3 were studied before and after irradiation with fast neutrons (En ≥ 1 MeV) at a fluence Φ = 5.5 × 1023 m–2. It was established that irradiation leads to the partial (∼5%) mutual disordering of the “lanthanum” and “manganese” sublattices. Ion displacements emerging at such radiation-induced disordering lead to the destruction of the Jahn–Teller mode Q2 responsible for A-type antiferromagnetism development in the initial sample. As a result, the antiferromagnet canted ferromagnet magnetic transformation is observed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Diffuse neutron scattering measurements were performed on quenched alloys with x = 0.31, 0.36, 0.39, 0.43 and 0.5, which belong to the transition region between ferromagnetism and antiferromagnetism. The nuclear and magnetic cross sections were separated, and Cowley short-range order atomic parameters determined. It was found that the superantiferromagnetic behaviour of these alloys occurred owing to the existence of the antiferromagnetic clusters of the -FeMn type caused by short-range order regions of the CuAu type.

Pressure-induced structural changes in irradiated YBa2cu3Ox (x=6.95) and uninradiated (x=6.91,6.54,6.39) samples have been measured by neutron powder diffraction in a hydrostatic liquid pressure cell. Tc has been measured for irradiated superconductors under pressure. The value of dTc/dP is found to be high (1.5 =bar). Increase in Tc is associated with charge transfer between the CuO2 planes and CuO chains which is reflected by anisotropy of crystal lattice compression.