The crystal structural and magnetic properties of the La3Co2MoO9 double perovskite ceramic sample have been studied by X-ray and neutron powder diffraction and magnetometry. Structural investigation indicated that sample is monoclinic perovskite with space group P21/n and unit cell parameters of a=5.5812(2) Å, b=5.7073(2)) Å, c=7.9279(3) Å, β=89.96(2)o, V=252.558(11)Å3 at room temperature. The two crystallographically-distinct 2d and 2c octahedral positions are occupied ordered by Co2+ (2d position) and Co2+ and Mo5+/Mo4+ (2c-position). Magnetometry data together with neutron powder diffraction study has shown that this perovskite is the ferrimagnetic (TC=147 K) with the uncompensated magnetic moment of 2 μB and the high value of coercive force HC (HC=75 kOe at 4.2 K}.

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 Bi(0.85)La(0.1)5FeO(3), oxides LiMn2O4 and Li0.9FePO4. The fast neutrons (E-eff > 0.1 MeV) have been used in a fluence range from 1 x 10(18) n/cm(2) to 2 x 10(20) n/cm(2) 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(B) in LiMnPO4 and LiFePO4 samples, while it is twice less for LiNi0.9Co0.1PO4.

The structural state and magnetic properties of nanocomposites formed by exfoliated graphite and 3d-transition metal (Co or Ni) particles have been studied.The exfoliated graphite was synthesized by thermal decomposition of the intercalated graphite C 2 Fx(BrF 3 ).The thus synthesized exfoliated graphite is multilayer graphene.The salt CoCl 2 6H 2 O (or NiCl 2 6H 2 O) was added to the graphene, and the mixture was agitated by a stirrer for half an hour and then heated in a hydrogen flow.The microstructure of the nanocomposites represents separated practically spherical inclusions of Co (or Ni) nanoparticles into a multilayer graphene matrix.The X-ray diffraction patterns of the nanocomposites with Co particles testify to their two-phase state at 293 K: they crystallize in low-temperature hexagonal and high-temperature cubic phases.At 78 K and 293 K, the magnetization curves of the nanocomposites, which are measured in pulsed magnetic fields of up to 100 kOe, look typically of ferromagnets.

The original version of the exchange-striction model of a ferrimagnet has been employed for calculating a number of magnetic properties of R Co 2 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 ErСо 2 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.

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 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(Co 0.9 Ga 0.1 ) 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 HoCo 2 is proposed.

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.

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.

We present the susceptibility and neutron diffraction data on multiferroic Ni3−xCoxV2O8 with x=0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order–disorder transition occurs at THTI=8.5K in both samples. Below THTI, 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).

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.

Multiferroic composites of ( x )NiFe 2 O 4 + (1- x )BaTiO 3 with x = 0.2, 0.3 and 0.4 and ( x )CoFe 2 O 4 + (1- x )BaTiO 3 with x = 0.2, and 0.4 have been synthesized by mixing NiFe 2 O 4 (CoFe 2 O 4 ) spinel and BaTiO 3 piezoelectric. Distribution of Ni (Co) ions on 8 a and 16 d positions of spinel lattice (space group F d -3 m ) 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 10 2 – 10 5 Hz. At low frequencies the dielectric permittivity decreased from ~940 for x = 0.2 to ~360 for 0.4.

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.

A study of crystal and magnetic structures, heat capacity, magnetic and magnetocaloric properties of Ho(Co1-х Feх)2 (with increasing x from 0 to 0. 2) intermetallic compounds has been undertaken. Phase composition was controlled by X-ray diffraction analysis. Neutron diffraction experiment was performed at temperatures of 78 and 293K. Magnetic properties were measured within the temperature range 5÷325K in magnetic fields up to 70 kOe. It was shown that considerable maximum broadenings on the temperature dependence of magnetic entropy change is observed with iron concentration increase. The avarage magnetic moment of Ho ions in their sublattice decreases from 10μB for HoCo2 to 9μB for Ho(Co0.8Fe0.2)2 that can be connected with the existence of the umbrella-like (canting) magnetic structure in Ho-sublattice.