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The nanoparticles with a pure cubic phase of isocubanite CuFe 2 S 3 are successfully synthesized for the first time. The particles are self-organized into the single crystalline nanocomposites with a shape of “bricks” which are well ordered in a certain anisotropic orientation. All bricks have nearly the same shape and dimensions and may be considered as monodispersed nanobricks. Magnetic measurements show paramagnetic behavior of the compound down to 4.2 K with the antiferromagnetic correlation between iron ions. An average magnetic moment is about 2.8–3.0 μ B per formula unit CuFe 2 S 3 . Mössbauer spectroscopy data reveal that the ferric ions in isocubanite are in the high-spin state (spin S =5/2) whereas the ferrous ions are in the intermediate-spin state ( S =1). The Fe 3+ and Fe 2+ ions are distributed randomly over tetrahedral sites and the electron exchange between these ions is absent. This can explain nonmagnetic behavior of isocubanite. In the suggested method, the combined nanocomposites containing the magnetic chalcopyrite CuFeS 2 and the nonmagnetic isocubanite CuFe 2 S 3 can be synthesized in a certain sequence. Such composites could be useful for the applied nanotechnology. [ABSTRACT FROM AUTHOR]

Electronic spin transitions of iron in the Earth's mantle minerals are of great interest to deep-Earth researchers because their effects on the physical and chemical properties of mantle minerals can significantly affect our understanding of the properties of the deep planet. Here we have studied the electronic spin states of iron in ringwoodite (Mg0.75Fe0.25)2SiO4 using synchrotron Mössbauer spec-troscopy in a diamond-anvil cell up to 82 GPa. The starting samples were analyzed extensively using transmission and scanning electron microscopes to investigate nanoscale crystal chemistry and local iron distributions. Analyses of the synchrotron Mössbauer spectra at ambient conditions reveal two non-equivalent iron species, (Fe2+)1 and (Fe2+)2, which can be attributed to octahedral and tetrahedral sites in the cubic spinel structure, respectively. High-pressure Mössbauer measurements show the disappearance of the hyperfine quadrupole splitting (QS) of the Fe2+ ions in both sites at approximately 45-70 GPa, indicating an electronic high-spin (HS) to low-spin (LS) transition. The spin transition exhibits a continuous crossover nature over a pressure interval of ~25 GPa, and is reversible under decompression. Our results here provide the first experimental evidence for the occurrence of the spin transition in the spinel-structured ringwoodite, a mantle olivine polymorph, at high pressures. [ABSTRACT FROM AUTHOR]

A thermal pyrolysis method has been developed to synthesize the tetragonal phase of chalcopyrite magnetic semiconductor CuFeS2 nanoparticles. All nanoparticles have the same anisotropic brick-like shape, and the “bricks” are self-organized in a certain orientation, creating well-ordered nanocomposites. High-resolution transmission electron microscopy and electron diffraction data show that every nanobrick is a single crystal with a layered atomic structure and characteristic dimensions of about 5nm×20nm in plane. Magnetic measurements support the antiferromagnetic spin structure and reveal the appearance of a small ferromagnetic component below 60K. Magnetic anomalies observed in the zero-field cooled magnetization curves at low temperatures may be related to an appearance of magnetic moment at the Cu ion site. The Mössbauer spectra show that only about 50% of Fe atoms are in the magnetically ordered α-phase of chalcopyrite. The remaining Fe is non-magnetic and may be located either in the γ-phase of chalcopyrite or in isocubanite. [ABSTRACT FROM AUTHOR]

Ferropericlase [(Mg,Fe)O] is one of the most abundant minerals of the earth's lower mantle. The high-spin (HS) to low-spin (LS) transition in the Fe2+ ions may dramatically alter the physical and chemical properties of (Mg,Fe)O in the deep mantle. To understand the effects of compression on the ground electronic state of iron, electronic and magnetic states of Fe2+ in (Mg0.75Fe0.25)O have been investigated using transmission and synchrotron Mössbauer spectroscopy at high pressures and low temperatures (down to 5 K). Our results show that the ground electronic state of Fe2+ at the critical pressure Pc of the spin transition close to T = 0 is governed by a quantum critical point (T = 0, P = Pc) at which the energy required for the fluctuation between HS and LS states is zero. Analysis of the data gives Pc = 55 GPa. Thermal excitation within the HS or LS states (T > 0 K) is expected to strongly influence the magnetic as well as physical properties of ferropericlase. Multielectron theoretical calculations show that the existence of the quantum critical point at temperatures approaching zero affects not only physical properties of ferropericlase at low temperatures but also its properties at P-T of the earth's lower mantle. [ABSTRACT FROM AUTHOR]

High‐quality Fe1–xGaxBO3 single crystals (0.0 ≤ x ≤ 1.0) in the form of basal plates were synthesized by the flux technique. The exact content of Fe and Ga and homogeneity of their distribution in the crystal structure were determined by energy‐dispersive X‐ray spectroscopy. The crystal structure was refined using single‐crystal X‐ray diffraction data. The electronic and magnetic properties were studied using Mössbauer spectroscopy. It is shown that even a small content of diamagnetic gallium leads to a rearrangement of the crystal structure and essentially changes the magnetic hyperfine parameters of the crystals. [ABSTRACT FROM AUTHOR]

The chemical interaction of Sn with H2 by X‐ray diffraction methods at pressures of 180–210 GPa is studied. A previously unknown tetrahydride SnH4 with a cubic structure (fcc) exhibiting superconducting properties below TC = 72 K is obtained; the formation of a high molecular C2/m‐SnH14 superhydride and several lower hydrides, fcc SnH2, and C2‐Sn12H18, is also detected. The temperature dependence of critical current density JC(T) in SnH4 yields the superconducting gap 2Δ(0) = 21.6 meV at 180 GPa. SnH4 has unusual behavior in strong magnetic fields: B,T‐linear dependences of magnetoresistance and the upper critical magnetic field BC2(T) ∝ (TC – T). The latter contradicts the Wertheimer–Helfand–Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of fcc SnH4 in non‐superconducting state exhibits a deviation from what is expected for phonon‐mediated scattering described by the Bloch‐Grüneisen model and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed. [ABSTRACT FROM AUTHOR]

We have synthesized the hexagonal pyrrhotite Fe1-xS nanodisks with the NiAs-type structure via thermal decomposition of ferrous chloride and thiourea in oleylamine. Mössbauer spectra analysis shows that the main part of iron of hexagonal pyrrhotite is in the Fe2+ valence state, and the spectrum has broadened half-maximum width due to the vacancy distribution. Magnetic measurements indicate that the magnetic moment configuration of nanodisks transforms from the ferrimagnetic to the ferromagnetic state at 400 K and magnetic moment disordering takes place at the Curie temperature, 580 K, at which ferromagnetic state transforms to paramagnetic structure. This magnetic transition behavior can be explained in terms of the iron vacancy rearrangement. [ABSTRACT FROM AUTHOR]

Ba3NbFe3Si2O14 single crystals of promising multiferroic properties from the langasite family have been grown by floating zone melting. The accurate high-resolution X-ray diffraction studies of this crystal were performed on a diffractometer with a two-dimensional CCD detector at 293 and 90.5 K. To compensate systematic measurement errors, two data sets were obtained independently for different sample orientations at each temperature. The structure refinement was performed based on averaged data sets with the following results: space group P321, Z = 1; a = 8.52421(8), c = 5.23372(5) Å at 293 K; and a = 8.5211(2), c = 5.2243(7) Å, at 90.5 K. The R factors of the model structure refinement were found to be R/wR = 1.15/1.29% for 4396 independent reflections at 293 K, and R/wR = 1.13/1.35% for 4203 reflections at 90.5 K. A displacement of magnetic ion Fe3+ in the 3f site was found with reducing temperature. It was also established from comparison of the structures of Ba3NbFe3Si2O14 and Ba3TaFe3Si2O14 that the mobility of the cation in the 3f sites changes with an isomorphic substitution of Nb cations by Ta in the octahedral sites. This can change the characteristics of the structure and magnetic helix responsible for multiferroic properties of the iron-containing langasites. An anomaly in thermal expansion is found in the Ba3NbFe3Si2O14 crystal. When the temperature is reduced, the compression ratio along the c axis is about two times larger than that along the a axis, which is not typical of other langasite-family crystals. [ABSTRACT FROM AUTHOR]

The crystal structure of samarium iron borate was analyzed with regard to growth conditions and temperature. The inclusion of about 7% Bi atoms in the crystals grown using the Bi2Mo3O12-based flux was discovered and there were no impurities in the crystals grown using the Li2WO4-based flux. No pronounced structural features associated with Bi inclusion were observed. The different absolute configurations of the samples grown using both fluxes were demonstrated. Below 80 K, a negative thermal expansion of the c unit-cell parameter was found. The structure of (Sm0.93Bi0.07)Fe3(BO3)4 belongs to the trigonal space group R32 in the temperature range 90-400 K. A decrease in the (Sm,Bi)--O, Sm--B, Sm--Fe, Fe--O, Fe--B and Fe--Fe distances is observed with a lowering of the temperature, B1--O does not change, B2--O increases slightly and the B2O3 triangles deviate from the ab plane. The strongest decrease in the equivalent isotropic atomic displacement parameters (Ueq) with decreasing temperature is observed for atoms Sm and O2, and the weakest is observed for B1. The O2 atoms have the highest Ueq values, the most elongated atomic displacement ellipsoids of all the atoms and the smallest number of allowed vibrational modes of all the O atoms. The largest number of allowed vibrational modes and the strongest interactions with neighbouring atoms is seen for the B atoms, and the opposite is seen for the Sm atoms. The quadrupole splitting Δ(T) of the paramagnetic Mo? ssbauer spectra increases linearly with cooling. The Ne' el temperature [TN = 31.93 (5) K] was determined from the temperature dependence of the hyperfine magnetic field Bhf(T), which has a non-Brillouin character. The easy-plane long-range magnetic ordering below TN was confirmed. [ABSTRACT FROM AUTHOR]

The crystal structure of samarium iron borate was analyzed with regard to growth conditions and temperature. The inclusion of about 7% Bi atoms in the crystals grown using the Bi2Mo3O12‐based flux was discovered and there were no impurities in the crystals grown using the Li2WO4‐based flux. No pronounced structural features associated with Bi inclusion were observed. The different absolute configurations of the samples grown using both fluxes were demonstrated. Below 80 K, a negative thermal expansion of the c unit‐cell parameter was found. The structure of (Sm0.93Bi0.07)Fe3(BO3)4 belongs to the trigonal space group R32 in the temperature range 90–400 K. A decrease in the (Sm,Bi)—O, Sm—B, Sm—Fe, Fe—O, Fe—B and Fe—Fe distances is observed with a lowering of the temperature, B1—O does not change, B2—O increases slightly and the B2O3 triangles deviate from the ab plane. The strongest decrease in the equivalent isotropic atomic displacement parameters (Ueq) with decreasing temperature is observed for atoms Sm and O2, and the weakest is observed for B1. The O2 atoms have the highest Ueq values, the most elongated atomic displacement ellipsoids of all the atoms and the smallest number of allowed vibrational modes of all the O atoms. The largest number of allowed vibrational modes and the strongest interactions with neighbouring atoms is seen for the B atoms, and the opposite is seen for the Sm atoms. The quadrupole splitting Δ(T) of the paramagnetic Mössbauer spectra increases linearly with cooling. The Néel temperature [TN = 31.93 (5) K] was determined from the temperature dependence of the hyperfine magnetic field Bhf(T), which has a non‐Brillouin character. The easy‐plane long‐range magnetic ordering below TN was confirmed.The crystal structure of samarium iron borate, SmFe3(BO3)4, grown by the solution‐melt technique using fluxes based on Bi2Mo3O12 and Li2WO4, was analyzed with regard to the synthesis conditions and temperature. The studies were carried out using energy‐dispersive X‐ray fluorescence spectroscopy, X‐ray spectral energy‐dispersive microanalysis, single‐crystal X‐ray structure analysis and Mössbauer absorption spectroscopy. The characteristic temperatures were calculated. [ABSTRACT FROM AUTHOR]

Neodymium iron borate NdFe3(BO3)4 is an intensively studied multiferroic with high electric polarization values controlled by a magnetic field. It is characterized by a large quadratic magnetoelectric effect, rigidity in the base plane and a rather strong piezoelectric effect. In this work, the atomic structure of (Nd0.91Bi0.09)Fe3(BO3)4 was studied by single‐crystal X‐ray diffraction in the temperature range 20–500 K (space group R32, Z = 3). The Bi atoms found in the composition partially substitute the Nd atoms in the 3a position; they entered the structure due to the growth conditions in the presence of Bi2Mo3O12. It was shown that in the temperature range 20–500 K there is no structural phase transition R32→P3121, which occurs in rare‐earth iron borates (RE = Eu–Er, Y) with an effective rare‐earth cation radius smaller than that of Nd. The temperature dependence of the unit‐cell c parameter reveals a slight increase on cooling below 90 K, which is similar to the results obtained previously for iron borates of Gd, Y and Ho. The atomic distances (Nd,Bi)—O, (Nd,Bi)—B, (Nd,Bi)—Fe, Fe—O, Fe—B and Fe—Fe in the iron chains and between chains decrease steadily with decreasing temperature from 500 to 90 K, whereas the B1(3b)—O distance does not change and the average B2(9e)—O distance increases slightly. There is a uniform decrease in the atomic displacement parameters with decreasing temperature, with a more pronounced decrease for the Nd(3a) and O2(9e) atoms. The O2(9e) atoms are characterized by the maximum atomic displacement parameters and the most elongated atomic displacement ellipsoids. The characteristic Debye and Einstein temperatures, and the static component in the atomic displacements were determined for cations using multi‐temperature diffraction data. It was shown that the Nd cations have the weakest bonds with the surrounding atoms and the B cations have the strongest. [ABSTRACT FROM AUTHOR]

[Display omitted] Here we report the high-pressure synthesis of a series of lanthanum–yttrium ternary hydrides obtained at pressures of 170–196 GPa via the laser heating of P 6 3 /mmc La–Y alloys with ammonia borane. As a result, we discovered several novel compounds: cubic hexahydride (La,Y)H 6 and decahydrides (La,Y)H 10 with a maximum critical temperature T C ∼ 253 K and an extrapolated upper critical magnetic field B C2 (0) of up to 135 T at 183 GPa. The current–voltage measurements show that the critical current density J C in (La,Y)H 10 is 12–27.7 kA/mm2 at 4.2 K, which is comparable with that of commercial superconducting wires such as NbTi and Nb 3 Sn. (La,Y)H 6 and (La,Y)H 10 are among the first examples of ternary high- T C superconducting hydrides. Our experiments show that part of metal atoms in the structures of recently discovered Im 3 ¯ m -YH 6 and Fm 3 ¯ m -LaH 10 can be replaced with lanthanum (∼70%) and yttrium (∼25%), respectively, with the formation of unique ternary superhydrides containing metal-encapsulated cages La@H 24 and Y@H 32 , which are specific for Im 3 ¯ m -LaH 6 and Fm 3 ¯ m -YH 10. This work demonstrates that hydrides, unstable in pure form such as LaH 6 and YH 10 , may nevertheless be stabilized at relatively low pressures in solid solutions with superhydrides having the desired structure. [ABSTRACT FROM AUTHOR]

• The quasi-one-dimensional ferromagnetism of Ni-Fe nanowires. • A high value of the magnetic anisotropy energy of Ni-Fe nanowires. • First time calculations by the generalized Stoner-Wohlfarth model. Nanowires of Ni 1−x Fe x compounds were obtained by electrochemical deposition in pores of flexible polymer track membranes with pore diameters of 30 and 70 nm. The elemental composition and growth conditions, allowing to control the length and aspect ratio of the nanowire, were established. Magnetic and Mössbauer spectroscopy measurements show that the nanowires have pronounced ferromagnetic properties, and the magnetic moments of Ni-Fe nanoparticles are oriented mainly along the wire axis. In particular, the nanowires with a length of about 10 μm and a diameter of 30 nm consist of magnetic domains about 20 nm in size with magnetic moments oriented predominantly along the axis of the nanowire. Such materials can be considered as quasi-one-dimensional nanostructured ferromagnetic systems. A new theoretical model was used to describe the magnetic properties and calculate the basic physical parameters of nanowires. [ABSTRACT FROM AUTHOR]

An accurate single‐crystal X‐ray diffraction study of bismuth‐containing HoFe3(BO3)4 between 11 and 500 K has revealed structural phase transition at Tstr = 365 K. The Bi atoms enter the composition from Bi2Mo3O12‐based flux during crystal growth and significantly affect Tstr. The content of Bi was estimated by two independent methods, establishing the composition as (Ho0.96Bi0.04)Fe3(BO3)4. In the low‐temperature (LT) phase below Tstr the (Ho0.96Bi0.04)Fe3(BO3)4 crystal symmetry is trigonal, of space group P3121, whereas at high temperature (HT) above 365 K the symmetry increases to space group R32. There is a sharp jump of oxygen O1 (LT) and O2 (LT) atomic displacement parameters (ADP) at Tstr. O1 and O2 ADP ellipsoids are the most elongated over 90–500 K. In space group R32 specific distances decrease steadily or do not change with decreasing temperature. In space group P3121 the distortion of the polyhedra Ho(Bi)O6, Fe1O6 and Fe2O6, B2O3 and B3O3 increases with decreasing temperature, whereas the triangles B1O3 remain almost equilateral. All BO3 triangles deviate from the ab plane with decreasing temperature. Fe–Fe distances in Fe1 chains decrease, while distances in Fe2 chains increase with decreasing temperature. The Mössbauer study confirms that the FeO6 octahedra undergo complex dynamic distortions. However, all observed distortions are rather small, and the general change in symmetry during the structural phase transition has very little influence on the local environment of iron in oxygen octahedra. The Mössbauer spectra do not distinguish two structurally different Fe1 and Fe2 positions in the LT phase. The characteristic temperatures of cation thermal vibrations were calculated using X‐ray diffraction and Mössbauer data. [ABSTRACT FROM AUTHOR]

An accurate X‐ray diffraction study of (Y0.95Bi0.05)Fe3(BO3)4 single crystals in the temperature range 90–500 K was performed on a laboratory diffractometer and used synchrotron radiation. It was established that the crystal undergoes a diffuse structural phase transition in the temperature range 350–380 K. The complexity of localization of such a transition over temperature was overcome by means of special analysis of systematic extinction reflections by symmetry. The transition temperature can be considered to be Tstr ≃ 370 K. The crystal has a trigonal structure in the space group P3121 at temperatures of 90–370 K, and it has a trigonal structure in the space group R32 at 375–500 K. There is one type of chain formed by the FeO6 octahedra along the c axis in the R32 phase. When going into the P3121 phase, two types of nonequivalent chains arise, in which Fe atoms are separated from the Y atoms by a different distance. Upon lowering the temperature from 500 to 90 K, a distortion of the Y(Bi)O6, FeO6, B(2,3)O3 coordination polyhedra is observed. The distances between atoms in helical Fe chains and Fe—O—Fe angles change non‐uniformly. A sharp jump in the equivalent isotropic displacement parameters of O1 and O2 atoms within the Fe—Fe chains and fluctuations of the equivalent isotropic displacement parameters of B2 and B3 atoms were observed in the region of structural transition as well as noticeable elongation of O1, O2, B2, B3, Fe1, Fe2 atomic displacement ellipsoids. It was established that the helices of electron density formed by Fe, O1 and O2 atoms may be structural elements determining chirality, optical activity and multiferroicity of rare‐earth iron borates. Compression and stretching of these helices account for the symmetry change and for the manifestation of a number of properties, whose geometry is controlled by an indirect exchange interaction between iron cations that compete with the thermal motion of atoms in the structure. Structural analysis detected these changes as variations of a number of structural characteristics in the c unit‐cell direction, that is, the direction of the helices. Structural results for the local surrounding of the atoms in (Y0.95Bi0.05)Fe3(BO3)4 were confirmed by EXAFS and Mössbauer spectroscopies. [ABSTRACT FROM AUTHOR]

Nanosystems for targeted delivery and remote-controlled release of therapeutic agents has become a top priority in pharmaceutical science and drug development in recent decades. Application of a low frequency magnetic field (LFMF) as an external stimulus opens up opportunities to trigger release of the encapsulated bioactive substances with high locality and penetration ability without heating of biological tissue in vivo. Therefore, the development of novel microencapsulated drug formulations sensitive to LFMF is of paramount importance. Here, we report the result of LFMF-triggered release of the fluorescently labeled dextran from polyelectrolyte microcapsules modified with magnetic iron oxide nanoparticles. Polyelectrolyte microcapsules were obtained by a method of sequential deposition of oppositely charged poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) on the surface of colloidal vaterite particles. The synthesized single domain maghemite nanoparticles integrated into the polymer multilayers serve as magneto-mechanical actuators. We report the first systematic study of the effect of magnetic field with different frequencies on the permeability of the microcapsules. The in situ measurements of the optical density curves upon the 100 mT LFMF treatment were carried out for a range of frequencies from 30 to 150 Hz. Such fields do not cause any considerable heating of the magnetic nanoparticles but promote their rotating-oscillating mechanical motion that produces mechanical forces and deformations of the adjacent materials. We observed the changes in release of the encapsulated TRITC-dextran molecules from the PAH/PSS microcapsules upon application of the 50 Hz alternating magnetic field. The obtained results open new horizons for the design of polymer systems for triggered drug release without dangerous heating and overheating of tissues. [ABSTRACT FROM AUTHOR]

• Structural phase transitions in the FeSe0.89S0.11 superconductor at high pressures up to 18.5 GPa. • Most sample part's recrystallization into the hexagonal phase (sp. gr. P63/mmc) at decompression. • Strong hysteresis of the structural properties during a phase transition under pressure. We report on the structural phase transitions in the FeSe 0.89 S 0.11 superconductor with T C = 11 K observed by powder synchrotron X-ray diffraction at high pressures up to 18.5 GPa under compression and decompression modes. It was found that at ambient pressure and room temperature, FeSe 0.89 S 0.11 has a tetragonal structure (space group P4/n). Under compression, in the region of 10 GPa, a phase transition from the tetragonal into the orthorhombic structure (sp. gr. Pnma) is observed, which persists up to 18.5 GPa. Our results strongly suggest that, at decompression, as the applied pressure decreases to 6 GPa and then is completely removed, most of the sample recrystallizes into the hexagonal phase of the structural type NiAs (sp. gr. P6 3 /mmc). However, the other part of the sample remains in the high pressure orthorhombic phase (sp. gr. Pnma), while the tetragonal phase (sp. gr. P4/n) is not restored. These observations illustrate a strong hysteresis of the structural properties of FeSe 0.89 S 0.11 during a phase transition under pressure. [ABSTRACT FROM AUTHOR]