D. Paccard

RM3Ga2 Compounds (R ≡ rare earth, M ≡ Co, Ni): A new structural series

Abstract X-ray diffraction on single crystals was used to establish the crystal structure of YCo 3 Ga 2 and YNi 3 Ga 2 . This hexagonal structure belongs to the P 6/ mmm space group. RCo 3 Ga 2 compounds with R ≡ La — Er and RNi 3 Ga 2 with R ≡ La — Tm crystallize with the same structure which is closely related to the hexagonal CaCu 5 -type structure.

Structure of YRh2Si: An ordered CeNi3 type

X-ray diffraction studies of single crystal YRh2Si were used to establish the crystal structure, with space group P6/mmc and lattice parameters a = 5.495 A, c = 15.030 A. YRh2Si with CeNi3-type structure is a member of the Rn +2 T3n +3M2n + 1 structural series (n = 1) with intergrown Mg2Cu3Si-type and CeCo3B2-type slabs.

Rare earth-iridium compounds with Pu5Rh3 and Y3Rh2 structure types: Members of a new structural series with formula R5n + 6T3n + 5

Abstract The structures of the rare earth-iridium compounds R 5 Ir 3 and R 3 Ir 2 were identified from X-ray powder diagrams. R 5 Ir 3 compounds (R  La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Y) crystallize with the tetragonal Pu 5 Rh 3 structure type. R 3 Ir 2 compounds (R  Gd, Tb, Dy, Ho, Er, Y) crystallize with the tetragonal Y 3 Rh 2 structure type. The Pu 5 Rh 3 type is a structure block shift variation of the W 5 Si 3 type. The W 5 Si 3 , Pu 31 Pt 20 and Y 3 Rh 2 structures are members of a structural series with the formula R 5 n + 6 T 3 n + 5 in which n takes the values ∞, 5 and 3 respectively.

RFexSi2 (R ≡ Tb, Dy, Ho, Er, Lu) structures with the non-stoichiometric TbFeSi2 type

X-ray diffraction studies on single crystals of HoFe0.5Si2 were used to establish the crystal structure, with space group Cmcm and lattice constants a = 4.0138(8) A, b = 15.7095(37) A, c = 3.8963(9) A. It is a non-stoichiometric TbFeSi2-type phase with defects, the transition metal site is half occupied by iron and the other sites are fully occupied. We observe the same structure with defects on single-crystal DyFe0.5Si2 and TbFe0.52Si2.

A new quaternary iron-rich phase stabilized by carbon: DyFe2SiC

Abstract X-ray diffraction studies of single crystal DyFe2SiC were used to establish the crystal structure, with space group Cmcm and lattice constants a = 3.712(0) A , b = 10.531(3) A , c = 6.863(1) A . The crystal structure is derived from the YNiAl2 type (Re3B-type derivative) with an ordered replacement of aluminium atoms by iron atoms and of nickel atoms by silicon atoms and with an addition of carbon atoms between the infinite columns of silicon centred DyFe2 prisms.

Magnetic properties of a new series of Nd-based compounds NdNi1−xCux

Abstract The magnetic properties of the NdNi 1− x Cu x compounds (0.4≤ x ≤ 1) with the FeB-type orthorhombic structure have been studied using electrical resistivity and magnetization measurements. For x ≤ 0.7, the compounds are ferromagnetic ( T C ≈ 35 K) with strong anisotropy, while the compositions with x = 0.9 and 1 are antiferromagnetic, suggesting the existence of complex magnetic structures. This evolution can be understood as a consequence of the modification of the magnetic interactions in large anisotropy compounds.

Magnetic structures of Nd2Fe2Si2C and Tb2Fe2Si2C

Abstract Magnetic properties of R2Fe2Si2C (with R = Nd, Tb) have been studied by means of neutron diffraction. An antiferromagnetic behaviour have been evidenced below 15 K for the Nd based compound and 45 K for the Tb based compound. The magnetic cell is twice the crystallographic one, with a propagation vector k = (0, 0, 1 2 ) . The main original feature of both structures is the non-colinearity between both R and Fe sublattices, the magnetic moments being nearly perpendicular.

Y3RhSi3: Member of the structural series with formula Rn + 2T2Sin + 2

X-ray diffraction examination of single crystals was used to establish the crystal structure of Y3RhSi3. The structure, which is isotypic with Sc3NiSi3 (monoclinic space group C2/m), consists of bands of four infinite columns of trigonal prisms connected by two infinite columns of yttrium or rhodium trigonal prisms. All these prisms are silicon centred. This compound belongs to a new series with the general formula Rn + 2T2Sn + 2 where n represents the number of trigonal prisms in each band.

Structure of ordered Gd2Co7-type Y4Rh9Si5

Single-crystal X-ray diffraction was used to establish the crystal structure of Y4Rh9Si5, (space group, R3m) with lattice parameters a = 5.496 A and c = 33.176 A. The structure is an ordered version of the Gd2Co7 type with rhodium and silicon occupying the corresponding cobalt sites. It consists of stacks of blocks corresponding to the CaCu5-type structure and the MgCu2-type structure.

R5T3 compounds (R ≡ rare earth; T ≡ Rh, Ir) with an Mn5Si3-type structure

Abstract X-ray diffraction on a single crystal was used to establish the crystal structure of Ho5Rh3. A hexagonal structure of the Mn5Si3 type with space group P63/mcm and lattice constants a = 8.100 A and c = 6.337 A was determined. Gd5Rh3, Tb5Rh3, Dy5Rh3, Er5Rh3, Tm5Rh3 and Lu5Rh3 are isostructural with Ho5Rh3. X-ray powder diagrams taken with a Guinier camera on the high temperature phase of R5Ir3 compounds (R ≡ Tb, Dy, Ho, Er, Tm, Lu) were indexed using Mn5Si3 structure parameters. A single-crystal study of Lu5Ir3 and Er5Ir3 showed weak superstructure reflections.