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The multiferroic RFe3(BO3)4 family is characterized by diverse magnetic, magnetoelectric, and magnetoelastic properties, the fundamental aspects of which are essential for modern electronics. The present research, using single-crystal X-ray diffraction (XRD) and Mössbauer spectroscopy (MS) in the temperature range of 25–500 K, aimed to analyze the influence of local atomic coordination on magnetoelectric properties and exchange and super-exchange interactions in RFe3(BO3)4. Low-temperature, single-crystal XRD data of the magnetically ordered phase of RFe3(BO3)4 at 25 K, which were obtained for the first time, were supplemented with data obtained at higher temperatures, making it possible to draw conclusions about the mechanism of the structural dynamics. It was shown that, in structures with R = Gd, Ho, and Y (low-temperature space group P3121), a shift in oxygen atoms (O2, second coordination sphere of R atoms) was accompanied by rotation of the B2O3 triangle toward R atoms at low temperatures, and by different rearrangements in iron chains of two types, in contrast to Nd and Sm iron borates (space group R32). These rearrangements in the structures of space group P3121 affected the exchange and super-exchange paths at low temperatures. The MS results confirm the influence of the distant environment of atoms on the magnetoelectric properties of rare-earth iron borates at low temperatures. [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]

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]

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]

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]

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]

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]

• 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]