Magnetic structures and magnetoelastic coupling of Fe-doped hexagonal manganites LuMn1-xFexO3 (0 < x < 0.3)

We have studied the crystal and magnetic structures of Fe-doped hexagonal manganites LuMn1-xFexO3 (x = 0, 0.1, 0.2, and 0.3) by using bulk magnetization and neutron powder diffraction methods. The samples crystalize consistently in a hexagonal structure and maintain the space group P63cm from 2 to 300 K. The N\'eel temperature TN increases continuously with increasing Fe-doping. In contrast to a single {\Gamma}4 representation in LuMnO3, the magnetic ground state of the Fe-doped samples can only be described with a spin configuration described by a mixture of {\Gamma}3 (P63'cm') and {\Gamma}4 (P63'c'm) representations, whose contributions have been quantitatively estimated. The drastic effect of Fe-doping is highlighted by composition-dependent spin reorientations. A phase diagram of the entire composition series is proposed based on the present results and those reported in literature. Our result demonstrates the importance of tailoring compositions in increasing magnetic transition temperatures of multiferroic systems.Comment: 18 pages, 9 figure

MnSnTeO6: A Chiral Antiferromagnet Prepared by a Two-Step Topotactic Transformation

MnSnTeO6, a new chiral antiferromagnet, was prepared both by topotactic transformation of the metastable rosiaite-type polymorph and by direct synthesis from coprecipitated hydroxides. Its structure and its static and dynamic magnetic properties were studied comprehensively both experimentally (through X-ray and neutron powder diffraction, magnetization, specific heat, dielectric permittivity, and ESR techniques) and theoretically (by means of ab initio density functional theory (DFT) calculations within the spin-polarized generalized gradient approximation). MnSnTeO6 is isostructural with MnSb2O6 (space group P321) and does not show any structural transition between 3 and 300 K. The magnetic susceptibility and specific heat exhibit an antiferromagnetic ordering at TN ≈ 9.8 K, which is confirmed by low-temperature neutron data. At the same time, the thermodynamic parameters demonstrate an additional anomaly on the temperature dependences of magnetic susceptibility χ(T), specific heat Cp(T) and dielectric permittivity ϵ(T) at T∗ ≈ 4.9 K, which is characterized by significant temperature hysteresis. Clear enhancement of the dielectric permittivity at T∗ is most likely to reflect the coupling of dielectric and magnetic subsystems leading to development of electric polarization. It was established that the ground state of MnSnTeO6 is stabilized by seven exchange parameters, and neutron diffraction revealed incommensurate magnetic structure with propagation vector k = (0, 0, 0.183) analogous to that of MnSb2O6. Ab initio DFT calculations demonstrate that the strongest exchange coupling occurs between planes along diagonals. All exchange parameters are antiferromagnetic and reveal moderate frustration. Copyright © 2020 American Chemical Society.The reported study was funded by Russian Science Foundation according to the research project nos. 18-12-00375 (A.K. and M.K.) for neutron studies and 17-12-01207 (E.Z. and S.S.) for magnetic, dielectric and specific heat studies as well as theoretical calculations. Sample preparation and diffraction studies by M.E., M.K., A.K., and V.N. were supported by the grant 18-03-00714 from the Russian Foundation for Basic Research. V.N. thanks the International Centre for Diffraction Data for Grant-in-Aid 00-15. A.V. and S.S. acknowledge the support by the Russian Ministry of Education and Science of the Russian Federation through NUST MISiS grant K2-2017-084 and by the Act 211 of the Government of Russia, contracts 02.A03.21.0004, 02.A03.21.0011, and 02.A03.21.0006. We thank Dr. Yu.V. Popov (SFU’s Shared Use Centre “Research in Mineral Resources and Environment”) for the EDX analysis

Теорія та практика менеджменту безпеки

У збірнику подано тези доповідей та виступів учасників Міжнародної науково-практичної конференції, присвяченої питанням теорії менеджменту безпеки, безпеки особистості, прикладним аспектам забезпечення соціальної, екологічної, економічної безпеки підприємств, питанням механізму забезпечення соціоекологоекономічної безпеки регіону, проблемам забезпечення національної безпеки

Neutron diffraction investigation of the crystal and magnetic structures in KCrF3 perovskite

KCrF3 represents another prototypical orbital-ordered perovskite, where Cr2+ possesses the same electronic configuration of 3d(4) as that of strongly Jahn-Teller distorted Mn3+ in many colossal magnetoresistance manganites. The crystal and magnetic structures of KCrF3 compound are investigated by using polarized and unpolarized neutron powder-diffraction methods. The results show that the KCrF3 compound crystallizes in tetragonal structure at room temperature and undergoes a monoclinic distortion with the decrease in temperature. The distortion of the crystal structure indicates the presence of cooperative Jahn-Teller distortion which is driven by orbital ordering. With decreasing temperature, four magnetic phase transitions are observed at 79.5, 45.8, 9.5, and 3.2 K, which suggests a rich magnetic phase diagram. Below T-N = 79.5 K, the Cr2+ moment orders in an incommensurate antiferromagnetic arrangement, which can be defined by the magnetic propagation vector (1/2 + delta, 1/2 + delta, 0). The incommensurate-commensurate magnetic transition occurs at 45.8 K and the magnetic propagation vector locks into (1/2, 1/2, 0) with the Cr moment of 3.34(5) mu(B), aligned ferromagnetically in (220) plane, but antiferromagnetically along [110] direction. Below 9.5 K, the canted antiferromagnetic ordering and weak ferromagnetism arise from the collinear antiferromagnetic structure while the Dzyaloshinskii-Moriya interaction and tilted character of the single-ion anisotropy might give rise to the complex magnetic behaviors below 9.5 K

Bell–like [Ga5] clusters in Sr₃Li₅Ga₅: synthesis, crystal structure and bonding analysis.

During the search for a possible replacement of the europium in the structure Eu3Li5+xGa5−x (x = 0.15) in order to facilitate the analysis of the chemical bonding in the bell–like [Ga5] clusters, the isostructural compound Sr3Li5Ga5 (space group R (Formula presented.) m, a = 9.6040(5) Å, c = 22.061(1) Å) was discovered. A detailed investigation of the bonding situation in the first five–membered nonconvex Ga cluster utilizing the electron localizability approach became possible, revealing not only first signs of a transition from a Zintl to a Wade cluster, but also the presence of a [Sr6] polycation. © 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH Gmb

From Zintl to Wade: Ba₃LiGa₅ – A Structure Pattern with Pyramidal Cluster Chains –[Ga₅]_n–

Investigation of the correlation between the crystal structure, electronegativity difference and valence electron concentration in intermetallic gallides lead to the discovery of the new compound Ba3LiGa5 (space group Immm, a = 6.2720(2) Å, b = 6.5872(2) Å, c = 12.6878(8) Å). A combination of quantum chemical bonding analysis with NMR study revealed the gallium substructure to be formed of chains built of the interconnected pyramidal [Ga5] clusters. Analysis of chemical bonding by means of the electron localizability approach confirmed the presence nido-[Ga5] Wade clusters. Lithium species are not only required for the purpose of charge compensation, but also – analogous to a transition metal – occupies partially the same crystallographic position as gallium. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA