Orthorhombic Pnma Symmetry Research Articles

Canted antiferromagnetism in an insulating lightly doped La1-xSrxMnO3 with x

We have investigated the magnetic structure of an insulating lightly doped ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ with x=0.04,0.125, and 0.17 with neutron scattering technique and bulk magnetization measurements. The magnetic structure of the x=0.04 sample at 5 K is a commensurate layer-type (A-type) antiferromagnetism with the propagation vector [010] and the moment of 3.7\ifmmode\pm\else\textpm\fi{}0.2${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Mn, being parallel to the [100] axis in the orthorhombic Pnma symmetry. In addition, a spontaneous magnetization of 0.28\ifmmode\pm\else\textpm\fi{}0.02${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Mn is observed at 8 K by magnetization measurement. By contrast, the x=0.125 sample exhibits a large ferromagnetic moment of 3.7\ifmmode\pm\else\textpm\fi{}0.2${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Mn and a small A-type antiferromagnetic component of 0.23\ifmmode\pm\else\textpm\fi{}0.1${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Mn, while the x=0.17 sample exhibits only a ferromagnetic component of 3.6\ifmmode\pm\else\textpm\fi{}0.2${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Mn. These results are consistent with a spin structure derived from the conventional double exchange mechanism, but rule out the possibility of a recently suggested spiral spin structure for the insulating ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ system. \textcopyright{} 1996 The American Physical Society.

Structure and Luminescence of the La1 − xGdx F 3 System

The trifluorides of La and Gd crystallize in different structures: is of the hexagonal tysonite (P31c) type, while crystallizes in orthorhombic (Pnma) symmetry. Solid solutions of the type exist in the hexagonal structure to and convert to the orthorhombic phase at . Lattice parameters are reported and the x‐ray excited luminescence of Gd3+ in these compounds is discussed with particular emphasis on the Gd3+ site symmetry difference in and in .

Heptamanganese tricarbide Mn7C3

A procedure was examined for the preparation of Mn7C3 by reaction of manganese dust with n-pentane at 850 °C and a reduced pressure. The identity of the product was confirmed by chemical and X-ray diffraction analysis; no other carbide was found to be present. The powder X-ray diffraction patterns were investigated in terms of the structure assignment either to the hexagonal P63mc or the orthorhombic Pnma symmetry. The reflection intensities fit better the latter structure, but the possibility of hexagonal indexing indicates that the octahedral structural elements do not arrange coherently during the synthesis. The composition of the products of hydrolysis is also consistent with the formula Mn7C3. The gaseous products contain hydrogen, methane, and a number of other hydrocarbons, mostly saturated, whose concentration decreases with increasing number of carbon atoms in the molecule. The concentration distribution of the hydrocarbons is discussed in terms of the radical mechanism of the hydrolysis; the data are borne out indicating that in Mn7C3 the covalent nature of the bonds is more pronounced than in salt type carbides.