G. Courbion

Magnetization, Mössbauer and neutron studies of α- and β-LiMnFeF6; evidence of idle spin behaviour in a ferrimagnet

Abstract The trigonal phases α- and β-LiMnFeF 6 have been investigated by neutron diffraction, magnetization measurements, remanent magnetization and Mossbauer spectroscopy in an external field. Below 158 K, α-LiMnFeF 6 is antiferromagnetic, with the Mn and Fe spins aligned antiparallel along the c axis. Below 113 K, the β-phase is ferrimagnetic, with the Mn(3e) and Fe(2d) spins aligned antiparallel along the c axis. Fe(1a) is weakly coupled to the net magnetization and behaves as an “idle spin”. The data are consistently analysed and discussed with respect to the connecting mode of the MF 6 octahedra.

Croissance cristalline par voie hydrothermale en presence d'acide fluorhydrique dans les systèmes MF-AlF3 ET NH4F-FeF3

Abstract Single crystals of MIAlF4 (MI = K, Rb, Tl, NH4, Cs) and NH4Fe2F6 were grown by the hydrothermal method (at 300°C and 1600 bar) starting with AlF3 and FeF3 in an aqueous MIF (5M) solution of hydroflourhydric acid (5M). The compounds were anhydrous and did not undergo any hydrolysis phenomena. Optimal conditions of growth are described and the crystallographic data are given for all the phases.

Structures of cesium containing fluorides, VI: The pyrochlore-related layer structures of Cs4CoCr4F18 and Cs4Cr5F18+x

The crystal structures of the hexagonal compounds Cs 4 CoCr 4 F 18 ( a = 720.3, c = 1076.1 pm) and Cs 4 Cr 5 F 18,24 ( a = 720.0, c = 1067.9 pm), both crystallizing in space group P 3 m 1, Z = 1, have been determined ( R g = 0.041 and 0.045, respectively). They exhibit a new triple layer arrangement of octahedra, which has the composition M 5 F 18 and derives from the RbNiCrF 6 -type pyrochlore structure. The overall average distances are M -F = 192.9 and 192.0 pm for the Co(II) and the Cr(II) compound, respectively, the smaller value of the latter being mainly due to the higher Cr(III) portion in it. The compensating anion excess is located and its influence discussed, as well as the evidence on the distribution of M (II) and M (III) ions on the lattice sites, including some hints on the presence of a Jahn-Teller distortion in the Cr(II) compound.

On new fluorides with the Jarlite-type structure: crystal structures of Na2Sr7Al6F34, Na2Sr6ZnFe6F34 and Ba7Ga6(F,OH)32 · 2H2O

Abstract New compounds, Na 2 Sr 7 Al 6 F 34 , Na 2 Sr 6 ZnFe 6 F 34 and Ba 7 Ga 6 (F,OH) 32 · 2H 2 O, have been prepared by hydrothermal synthesis in HF solution and by the chloride flux method. The crystal structures have been resolved by X-ray diffraction. All the phases present structures of the Jarlite type in spite of having a different unit cell for the iron phase. The structures of the two first compounds are characterized by [Na 2 Al 6 F 34 ] n 14 n − or [NaZnFe 6 F 34 n 13 n − sheets of octahedra connected by Sr or [Sr, Na] polyhedra whereas the hydrated fluoride exhibits [Ga 3 (F,OH) 16 ] 7− isolated octahedra trimers separated by Ba ions and water molecules. Structural correlations are made with other Jarlite type phases and with structures involving ‘independent’ fluoride ions.

ESR study of Cr3+ and Fe3+ ions in KGaF4 single crystals

Abstract KGaF 4 ( Pnma , a = 12.211(7), A, b = 7.496(2), A, c = 7.635(3), A, Z = 8) accurate X-ray structure determination has been carried out from 1754 reflections at room temperature ( R = 0.0256, R w = 0.0312). An accurate determination of spin Hamiltonian parameters for Cr 3+ and Fe 3+ ions in this host compound has been achieved. Intrinsic superposition model parameters are deduced and the validity of the model is discussed in this low-symmetry case. A structural phase transition occurring at about 465 K has been detected.