CHARGE TRANSFER BETWEEN POSITIVE ALKALI IONS AND ATOMS

The total cross sections for resonant charge exchange have been measured as a function of energy in the range from 10 to 500 eV for the Cs{sup +}-Cs, Rb{sup +}-Rb, and K{sup +}-K systems. The agreement with certain data obtained at higher energies for these systems, and with theoretical cross sections of Smirnov is satisfactory

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

Co(NO3)2 as an Inverted Umbrella-type Chiral Noncoplanar Ferrimagnet

The low-dimensional magnetic systems tend to reveal exotic spin-liquid ground states or form peculiar types of long-range order. Among systems of vivid interest are those characterized by the triangular motif in two dimensions. The realization of either ordered or disordered ground state in triangular, honeycomb, or kagome lattices is dictated by the competition of exchange interactions, also being sensitive to anisotropy and the spin value of magnetic ions. While the low-spin Heisenberg systems may arrive to a spin-liquid long-range entangled quantum state with emergent gauge structures, the high-spin Ising systems may establish the rigid noncollinear structures. Here, we present the case of chiral noncoplanar inverted umbrella-type ferrimagnet formed in cobalt nitrate Co(NO3)2 below TC=3K with the comparable spin and orbital contributions to the total magnetic moment. © 2020 American Physical Society.This work has been supported by Russian Scientific Foundation, Grant No. 19-42-02010 and by Russian Foundation for Basic Research (RFBR) Grants No. 18-52-52005, No. 18-502-12022, No. 19-02-00015, and No. 19-03-01059. We acknowledge support by the Russian Ministry of Science and Higher Education, Contracts No. 02.A03.21.0004, No. 02.A03.21.0006, and No. 02.A03.21.0011. O.V.M. and A.N.V. acknowledge support by NUST “MISiS,” Grant No. K2-2020-008. We acknowledge the support of Hochfeld Magnetlabor Dresden at Helmholtz Zentrum Dresden Rossendorf, member of the European Magnetic Field Laboratory (EMFL). B.L. acknowledges the support of DFG through Project No. B06 of SFB 1143 (ID No. 247310070). J.-Y.L. was supported by Taiwan MOST Grant No. 107-2923-M-009-001-MY3 and by the center for Emergent Functional Matter Science of NCTU from the Featured Areas Research Center program within the framework of the Higher education Sprout Project by the Ministry of Education (MOE) in Taiwan. M.A.-H. acknowledges the support from the Swedish Research Council Grant No. (VR) 2018-05339. I.V.S. was supported by Program AAAA-A18-118020190095-4 (Quantum)

A₂MnXO₄ Family (A = Li, Na, Ag; X = Si, Ge): Structural and Magnetic Properties

Four new manganese germanates and silicates, A₂MnGeO₄ (A = Li, Na) and A₂MnSiO₄ (A = Na, Ag), were prepared, and their crystal structures were determined using the X-ray Rietveld method. All of them contain all components in tetrahedral coordination. Li₂MnGeO₄ is orthorhombic (<i>Pmn</i>2₁) layered, isostructural with Li₂CdGeO₄, and the three other compounds are monoclinic (<i>Pn</i>) cristobalite-related frameworks. As in other stuffed cristobalites of various symmetry (<i>Pn</i> A₂MXO₄, <i>Pna</i>2₁ and <i>Pbca</i> AMO₂), average bond angles on bridging oxygens (here, Mn–O–X) increase with increasing A/X and/or A/M radius ratios, indicating the trend to the ideal cubic (<i>Fd</i>3̅<i>m</i>) structure typified by CsAlO₂. The sublattices of the magnetic Mn²⁺ ions in both structure types under study (<i>Pmn</i>2₁ and <i>Pn</i>) are essentially the same; namely, they are pseudocubic eutaxy with 12 nearest neighbors. The magnetic properties of the four new phases plus Li₂MnSiO₄ were characterized by carrying out magnetic susceptibility, specific heat, magnetization, and electron spin resonance measurements and also by performing energy-mapping analysis to evaluate their spin exchange constants. Ag₂MnSiO₄ remains paramagnetic down to 2 K, but A₂MnXO₄ (A = Li, Na; X = Si, Ge) undergo a three-dimensional antiferromagnetic ordering. All five phases exhibit short-range AFM ordering correlations, hence showing them to be low-dimensional magnets and a magnetic field induced spin-reorientation transition at <i>T</i> < <i>T</i>_N for all AFM phases. We constructed the magnetic phase diagrams for A₂MnXO₄ (A = Li, Na; X = Si, Ge) on the basis of the thermodynamic data in magnetic fields up to 9 T. The magnetic properties of all five phases experimentally determined are well explained by their spin exchange constants evaluated by performing energy-mapping analysis