The distribution of Co2+ ions over sublattices and structurally nonequivalent positions in the unit cell of the crystal lattice of a single crystal of lithium gallium spinel Li0.5Ga2.5O4 is shown. This distribution determines the properties of both mono- and nanocrystalline substances. The distribution is obtained by a special technology and is manifested in the electron paramagnetic resonance (EPR) spectra. The distribution of Co2+ ions depends on the structural and magnetic nonequivalence. The structural and magnetic nonequivalence causes a multiminimum behavior of the crystal field potential in the unit cells of single crystals at the locations of Co2+ ions. The Co2+ ions are found in complexes with tetrahedral and octahedral oxygen ions. Three types of EPR spectra of Co2+ ions have been found and investigated. The Co_tetr^2 + spectrum is attributed to the Co2+ ion, which replaces the Ga3+ ion located in a tetrahedral oxygen environment. The spectrum of the Co_oct^2 + ion located in the crystal field with axial symmetry belongs to the Co2+ ion replacing the Li+ ion located in an octahedral oxygen environment. The spectrum of the Co_oct^2 + ion located in a low symmetry crystal field belongs to the Co2+ ion replacing the Ga3+ ion located in an octahedral oxygen environment. The nearest cationic environment of the ion creates rhombic distortions due to the different valence numbers of Li+ and Ga3+. The results of studying the angular dependences of the spectra show the presence of four and twelve magnetically nonequivalent positions in the unit cells.

In the low temperature region, a change in the magnetic state was detected in the new NaNiFe2(VO4)3 magnetic compound, confirmed by the results of experimental study by gamma resonance and magnetometry methods. The formation of disordered magnetism in multicomponent vanadate is facilitated by the features of the crystal structure, in which magnetically active cations occupy several crystallographically non-equivalent mixed positions with uneven filling with iron and nickel ions.

A new magnetic compound NaZnFe2(VO4)3 obtained by solid-phase synthesis has been studied using X-ray diffraction, Mössbauer spectroscopy, electron paramagnetic resonance, measurement of the temperature dependence of the dielectric permeability, and magnetometry. The crystalline structure of NaZnFe2(VO4)3 is described by a triclinic spatial group of symmetry P1 with the parameters of an elementary crystalline chain: a = 6.74318 (7) Å, b = 8.1729 (1) Å, c = 9.8421 (1) Å, α = 106.2611 (9)º, β = 104.55 (1)º, γ = 102.337 (1)º, V = 479.88 (1) Å3, Z = 2. Magnetic Fe3+ cations in the cell occupy six positions populated together with diamagnetic Zn2+ cations, which leads to states of magnetic inhomogeneity and local violation of charge neutrality. Data from resonance and magnetic studies of NaZnFe2(VO4)3 confirm the main role of high-spin Fe3+ iron cations in the formation of magnetism with competing exchange magnetic interactions and a high value of the frustration index. It is shown that the magnetic subsystem of a sample with a negative asymptotic Neel temperature undergoes a magnetic transition from the paramagnetic state to the magnetic state of the spin glass when the temperature decreases. T.V. Drokina 1, M.S. Molokeev M.C. 1, 2, D.A. Velikanov 1, O.A. Bayukov 1, A.M. Vorotynov 1, A.L. Freidman 1, G.A. Petrakovskii 1 1 L.V. Kirensky Institute of Physics, Federal Research Center KSC Siberian Branch of Russian Academy of Science, Krasnoyarsk, 660036, Russia 2 Siberian Federal University, Krasnoyarsk, 660074, Russia

The study is part of biomedical nanotechnology and is carried out by probing these systems using the Electronic Spin Resonance (ESR) method. The paper investigates glass ionomer cement powder widely used in dental practice Glass ionomer cement CX - Plus Triplekit - TM. For analysis of properties of glass-ionomer cement ESR radiospectroscopy is used in the range from low (T=4.2K) to room (T=300K) temperatures. A new characteristic of compounds with nanocomplexes of magnetic iron ions Fe3+ is applied.

In the low temperature region, a change in the magnetic state was detected in the new NaNiFe2(VO4)3 magnetic compound, confirmed by the results of experimental study by gamma resonance and magnetometry methods. The formation of disordered magnetism in multicomponent vanadate is facilitated by the features of the crystal structure, in which magnetically active cations occupy several crystallographically non-equivalent mixed positions with uneven filling with iron and nickel ions. Keywords: multicomponent vanadates, magnetic properties, spin disorder.

The study is part of nanomedical biotechnology and is carried out by probing these systems using the Electronic Spin Resonance (ESR) method. The paper investigates Glass Ionomer Cement powder widely used in dental practice Glass Ionomer Cement C-Plus Triplekit-TM. To assess the quality of Glass Ionomer Cement and use ESR radiospectroscopy in the range from low (T=4.2 K) to room (T=300 K) temperatures. A new characteristic of compounds with nanocomplexes of magnetic iron ions Fe 3+ is applied. Key words: Electronic Spin Resonance (ESR), nanocrystals, crystal field potential, intensity of ESR lines.

Методом твердофазного синтеза получено новое магнитное соединение NaNiFe2(VO4)3, приведены результаты изучения методами рентгеновской дифракции, гамма-резонанса и магнитометрии. Кристаллическая структура многокомпонентного ванадата описывается триклинной пространственной группой симметрии P1. Элементарная ячейка содержит шесть неэквивалентных смешанных катионных позиций, занятых разновалентными ионами переходных металлов железа Fe3+ и никеля Ni2+, что способствует реализации состояния с локальным нарушением зарядовой нейтральности. Кроме того, обнаружено наличие двух типов позиций атомов железа: с кислородным окружением как в виде октаэдров, так и квадратных пирамид с неравновероятной их заселенностью железом и никелем. Ход температурной и полевой зависимостей намагниченности в широком температурном интервале характерен для парамагнетика, содержащего ферромагнитные кластеры. Ключевые слова: многокомпонентные ванадаты, кристаллическая структура, магнитные свойства.

Polycrystalline HoFeTi2O7 samples were obtained by solid-phase synthesis and studied by X-ray diffraction, gamma resonance, and SQUID methods. The characteristics of structural properties are presented, indicating the distribution of iron atoms over nonequivalent crystallographic positions and their uneven filling in the positions mixed with titanium. Spin disorder formed by mixing magnetic and nonmagnetic ions, spatial inhomogeneity of interactions that determine the magnetic structure in the crystal leads to the formation of competing exchange magnetic interactions between the nearest neighbors, frustration of magnetic bonds and the absence of long-range magnetic order. It has been shown that the temperature dependence of the static magnetic susceptibility at low temperatures has features characteristic of the spin glass magnetic state.

Polycrystalline samples of HoFeTi 2 O 7 were obtained by solid-phase synthesis and investigated using X-ray diffraction, gamma resonance, and SQUID measurements. Characteristics of the structural properties are presented, which give an evidence of the distribution of iron atoms among nonequivalent crystallographic positions and of the nonuniform populating of positions mixed with titanium by the iron atoms. Spin disorder caused by mixing of magnetic and nonmagnetic ions, spatial nonuniformity of the interactions defining the magnetic structure in the crystal lead to formation of concurrent magnetic exchange interactions between the nearest neighbors, frustration of magnetic couplings, and loss of the long-range magnetic ordering. The temperature dependence of the magnetic susceptibility at low temperatures was shown to have some peculiarities typical of the magnetic state of spin glass.

The structural, thermal, static magnetic, and resonance properties of the low-dimensional NaCuFe2(VO4)3 compound obtained by the solid-phase synthesis have been investigated. In the temperature range of 110–300 K, the electron spin resonance in the X band with a g factor of 2.008 has been detected. The magnetic properties of a sample with a high frustration level in the paramagnetic, antiferromagnetic, and disordered states have been examined. A shift of the Néel temperature to the high-temperature region in an external magnetic field has been observed. The origin of the disordered magnetism in NaCuFe2(VO4)3 are discussed. The features of substitution of sodium for lithium on the physical properties of the ACuFe2(VO4)3 (A = Na, Li) system have been established. It is shown that the chemical pressure changes the crystal lattice parameters, spacings between magnetic ions, and crystallite size, which is reflected in the physical properties of the material.

The results of the study of structural, thermal, static magnetic and resonance properties of the low-dimensional compound NaCuFe2(VO4)3 prepared by the standard solid-phase reaction method are presented. In the temperature range 110–300 K and in the X-band, an electron paramagnetic resonance was observed, characterized by a g-factor equal to 2.008. The magnetic properties of the sample with a high level of frustrations in the paramagnetic, antiferromagnetic, and disordered states are investigated. A shift of the Néel temperature to high temperatures under the influence of an external magnetic field was detected. The reasons for the appearance of disordered magnetism in NaCuFe2 (VO4) 3 are discussed. The features of the effect of sodium substitution by lithium on the physical properties of the ACuFe2 (VO4) 3 (A = Na, Li) system are revealed. It is shown that under the influence of chemical pressure there is a transformation of lattice parameters, distances between magnetic ions, crystallite size, which leads to a change in physical properties.

We report on the synthesis conductions and results of experimental investigations of the crystal structure and magnetic properties of a new magnetic compound YbFeTi 2 O 7 . According to the X-ray diffractometry data, the crystal structure of the investigated compound is described by the rhombic space group Pcnb with unit cell parameters of a = 9.8115(1) Å, b = 13.5106(2) Å, and c = 7.31302(9) Å and atomic disordering in the distribution of iron ions Fe 3+ over five structural sites. The magnetic measurements in the lowtemperature region revealed a kink in the temperature dependence of the magnetic moment and its dependence on the sample magnetic prehistory. The experimental results obtained suggest that with a decrease in temperature the sample passes from the paramagnetic state to the spin-glass-like magnetic state characterized by a freezing temperature of T f = 4.5 K at the preferred antiferromagnetic exchange coupling in the sample spin system. The chemical pressure variation upon replacement of rare-earth ion R by Yb in the RFeTi 2 O 7 system does not change the crystal lattice symmetry and magnetic state.

AbstractWe report on the synthesis conductions and results of experimental investigations of the crystal structure and magnetic properties of a new magnetic compound YbFeTi_2O_7. According to the X-ray diffractometry data, the crystal structure of the investigated compound is described by the rhombic space group Pcnb with unit cell parameters of a = 9.8115(1) Å, b = 13.5106(2) Å, and c = 7.31302(9) Å and atomic disordering in the distribution of iron ions Fe^3+ over five structural sites. The magnetic measurements in the lowtemperature region revealed a kink in the temperature dependence of the magnetic moment and its dependence on the sample magnetic prehistory. The experimental results obtained suggest that with a decrease in temperature the sample passes from the paramagnetic state to the spin-glass-like magnetic state characterized by a freezing temperature of T _ f = 4.5 K at the preferred antiferromagnetic exchange coupling in the sample spin system. The chemical pressure variation upon replacement of rare-earth ion R by Yb in the RFeTi_2O_7 system does not change the crystal lattice symmetry and magnetic state.

The experimental studies on R3+Fe3+Ti2O7 (R=Sm, Gd, Tb, Tm, Dy) magnetic properties evidence the low temperature spin glass state in all compounds. The possibility of rare-earth cation substitution allows the investigation of the role of magnetic iron Fe3+ ions and rare earth R3+ ions subsystems in a ground state formation in these oxide compounds.

A new magnetic compound NaNiFe 2 (VO 4 ) 3 has been obtained by the solid-phase synthesis and studied by X-ray diffractometry, nuclear gamma resonance, and magnetometry. The crystal structure of multicomponent vanadate is described by a triclinic symmetry space group P 1. The unit cell contains six nonequivalent mixed cationic positions occupied by different-valence ions of transition metals, iron Fe 3+ and nickel Ni 2+ , which facilitates the implementation of a state with the local charge neutrality violation. In addition, two types of iron atom sites have been found, which have an oxygen environment in the form of octahedra and square pyramids with their nonequiprobable population by iron and nickel. The temperature and field dependences of the magnetization have been found to be typical of a paramagnet containing ferromagnetic clusters in a wide temperature range.

The properties of Na x Li1–x FeGe2O6 (x = 0.1–0.9) solid solutions obtained via a solid-phase synthesis have been measured by X-ray diffraction, calorimetry, and magnetic method. The order–disorder transformations in low-dimensional Na x Li1–x FeGe2O6 (x = 0.1–0.9) spin systems with predominately antiferromagnetic exchange interaction have been revealed in the low-temperature susceptibility dependences. The study of thermal and physical properties has confirmed that substituting the sodium ions with the lithium ones induces the first-order structural phase transitions of the displacement type which are characterized by a symmetry change in monoclinic crystals from high-temperature C2/c space group to low-temperature P21/c space group.

The compounds RFeTi2O7 (R=Lu and Tb) crystallize at room temperature in centrosymmetric orthorhombic space group Pcnb. There are five non-equivalent positions of the iron ions: the two positions, Fe’ and Fe”, in the octahedron consisting of the Fe’ tetrahedron and Fe” five-vertex polyhedron and the three positions, Fe1, Fe2 and Fe3 in the mixed Fe-Ti octahedra [1]. The populations of the mixed Fe-Ti sites are different. The crystal structure features lead to atomic disorder in the distribution of the magnetic ions in this compound. From low temperature heat capacity, magnetization and frequency dependent ac susceptibility we conclude that both compounds undergo a spin glass transition at TSG=4.5 and 6K for R =Lu and Tb, respectively. Since Lu is not magnetic, in RFeTi2O7 the spin glass behavior is caused by the disordered distribution of the magnetic Fe3+ ions in the different crystallographic positions. The substitution of the magnetic and highly anisotropic Tb ion instead of Lu increases TSG because of the additional Tb-Fe exchange interaction, while the critical exponent of the frequency dependence on temperature hardly varies. The spin glass behavior in these crystalline compounds is caused by the presence of competitive interactions that lead to frustration.

The possibility of cation substitution in pyroxenes allows the investigation the gradual change of structural and magnetic properties under doping in these compounds. Here, Na0.5Li0.5FeGe2O6 was prepared by the standard solid-phase reaction method and has been investigated using X-ray and neutron powder diffraction, and further characterized by magnetic and calorimetric measurements. The crystal structure of Na0.5Li0.5FeGe2O6 at 300K is monoclinic C2/c (a=10.0333(1), b=8.8136(1), c=5.5295(9)Å, β=108.921(1)°). Calorimetric investigations indicate a displacive first order phase transition at T=271±1K which is accompanied by the appearance of superstructure reflections in the X-ray patterns. At this transition Na0.5Li0.5FeGe2O6 undergoes a space group change from C2/c to P21/c (a=9.9692(3), b=8.8545(3), c=5.4752(2)Å, β=108.494(1)°). Magnetic order has been found below the Néel temperature TN≈18K and has been refined from neutron diffraction. The quasi-low-dimensional magnetic spin system Na0.5Li0.5FeGe2O6 exhibits a collinear antiferromagnetic structure with the space group Pa21/c and the doubling of the unit cell along the crystallographic a-axis of the pyroxene crystal (propagation vector k=(1/2, 0, 0)). The critical modes which are responsible for the phase transition from C2/c to P21/c symmetry and for the magnetic transition from paramagnetic to antiferromagnetic state have been determined and their role in the transition is described. They are also the relevant mechanism driving the magnetic order in LiFeGe2O6.