On the synthesis and characterization of a new manganite type CMR material: La0.7Hg0.3MnO3

A new manganite type CMR material, La_0.7Hg_0.3MnO₃ has been successfully synthesized and has been found to exhibit magnetoresistance (≈9%) at low fields (≈1.5 kG). The synthesis has been carried out through a solid state reaction route consisting of the formation of La_0.7MnO₃ followed by diffusion of Hg leading to La_0.7Hg_0.3MnO₃. The as grown samples are polycrystalline and correspond to an orthorhombic unit cell with the lattice parameters; a=5.5183 Å, b=5.6383 Å and c=7.5368 Å. The typical grain size as revealed by scanning electron microscopy is in the range of 0.5–2 μm. The ρ–T behaviour shows a peak at T_IM=227 K. The ρ–T behaviour above this temperature corresponds to that of an insulator and below this to that of a metal. The ρ–T behaviour remains unaltered when a magnetic field (H_dc=1.5 kG) is applied. However, with this magnetic field a drop in the resistivity is observed up to 77 K. At room temperature the magnetoresistance ratio (MRR) is too small but it steadily increases as the temperature is decreased. Thus, MRRs at 227.13 and 77 K are 3.41 and 9.05%, respectively, in an applied field of H_dc=1.5 kG. At a given temperature the variation in MRR with field H_dc is rapid at lower field values (H_dc<1.2 kG) and scales linearly for higher field values (H_dc>1.2 kG). It may be mentioned that the present work on the synthesis and magnetoresistance behaviour of La_0.7Hg_0.3MnO₃, is the first of its type.     

Crystal and magnetic structures of Laves phase compound NdCo2 in the temperature range between 9 and 300 K

The crystal and magnetic structures of the Laves phase compound NdCo₂ in the temperature range from 9 to 300 K are determined by Rietveld refinement technique, using high-resolution neutron powder diffraction data. The compound crystallizes in space group above the magnetic ordering temperature T_C (≈100 K), in space group I4₁/amd below T_C and in space group Imma below the tetragonal–orthorhombic structural/magnetic transitions at T_M ≈ 42 K. The assignment of the space groups to the crystal structures of NdCo₂ in different temperature ranges complies with the reported Mössbauer studies. Detailed information of the crystal and magnetic structures of NdCo₂ at different temperatures are reported.     

HfFe6Ge6-type YbMn6Ge6−xGax compounds (0.07≤x<0.72) with large magnetocrystalline anisotropy

The HfFe₆Ge₆-type YbMn₆Ge_6−xGa_x solid solution (0.07≤x≤0.72) has been studied by X-ray diffraction, microprobe analysis and powder magnetization measurements. All the compounds order antiferromagnetically between T_N=481 K for x=0.07 and T_N=349 K for x=0.72 and display more or less pronounced spontaneous magnetization at lower temperature. The corresponding Curie points increase from 40 K for x=0.07 to 319 K for x=0.72. The maximum magnetization values of the Ga-rich compounds (M≈5 μ_B/f.u. at 6 K) is compatible with a ferrimagnetic order of the Mn and Yb sublattices whereas the smaller values measured in the Ga-poor compounds suggest the stabilization of non-colinear magnetic structures. All the studied compounds are characterized by rather large coercive fields at low temperature (4.0≤H_c≤8.2 kOe).     

Magnetic structures of R2RhSi3 (R=Ho, Er) compounds

Powder X-ray and neutron diffraction and magnetic measurements have been performed on R₂RhSi₃ (R=Ho and Er) compounds at low temperatures. The compounds crystallize in a derivative of the hexagonal AlB₂-type structure. The crystal structure parameters have been refined on the basis of the X-ray and neutron diffraction patterns collected in the paramagnetic region. These compounds are antiferromagnets with Néel temperatures of 5.2 K for Ho₂RhSi₃ and 5 K for Er₂RhSi₃. Both compounds exhibit collinear magnetic structures, described by the propagation vector k=(1/2,0,0) for Ho₂RhSi₃ and k=(0,0,0) for Er₂RhSi₃. This magnetic order is stable in the temperature range between 1.5 K and the Néel temperature.     

Investigation of the titanium–indium system

The phase diagram of the Ti–In system was determined using DTA, XRD and EDX analyses. The existence of the phases Ti₂In₅ [Mn₂Hg₅ type structure, space group P4/mbm, a=0.99995(3), c=0.29960(2) nm] and Ti₃In [Ni₃Sn type structure, space group P6₃/mmc, a=0.5978(1), c=0.4812(1) nm] was confirmed. The phase previously labeled Ti₃In₂ was found to exist in a narrow homogeneity region near Ti₅₆In₄₄. Rietveld refinement of the XRD powder pattern yielded solutions compatible with a Cu₃Au-type or a BiIn-type crystal structure, but not with a CuAu-type crystal structure. Furthermore, at 38.5 at.% In, a new phase was observed having a γ-brass related crystal structure [Ti₈In₅, space group , a=0.99578(6) nm]. The intermetallic phases were formed by a cascade of peritectic reactions ending in a eutectic at >99 at.% indium between Ti₂In₅ and (In) at 0.4 K below the melting temperature of pure indium.     

Crystal structure and physical properties of ternary compounds RPt3B, R=La, Pr, Nd

The crystal structure of a new series of ternary rare-earth platinum borides RPt₃B (R=La, Pr, Nd) has been studied by X-ray powder diffraction analyses from the ‘as-cast’ alloys. The tetragonal CePt₃B structure type, space group P4mm (No. 99), has been confirmed for all compounds. Rietveld refinements for the two compounds, PrPt₃B and NdPt₃B, were performed. LaPt₃B is a temperature-independent Pauli-type paramagnet from room temperature down to 4 K. PrPt₃B orders antiferromagnetically at T_N=15 K followed by a ferromagnetic spin flip at T_C=5 K, whereas NdPt₃B exhibits an antiferromagnetic spin alignment at a Néel temperature T_N=7 K. The temperature dependence of the electrical resistivity, ρ(T), reflects the metallic character of these compounds. Furthermore the characteristic changes of slope of ρ(T) plots prove the magnetic transitions.     

Materials with layered structures X: subsolidus phase diagram of the system FeIn2S4–FeIn2Se4

The system (1−x)FeIn₂S₄–xFeIn₂Se₄ has been investigated by X-ray powder methods. The subsolidus phase diagram is constructed in the temperature interval 600–1000°C. The spinel type FeIn₂S₄ exhibits a phase width up to the composition FeIn₂S₃Se and the layered FeIn₂Se₄ is formed for 1≥x≥0.65. A new layered compound is formed for 0.55≥x≥0.4 which crystallizes at temperatures below 850°C in an -FeGa₂S₄ structure with a=363.6 pm and c=1207.1 pm (x=0.5) for the hexagonal cell and at higher temperatures in the MgAl₂S₄-type with a=393.9 pm and c=3843.2 pm (x=0.5) for the hexagonal cell. Both structures have been refined by the Rietveld-method. All phase boundaries are nearly independent from temperature.     

New RRh5Ge3 compounds of the new SmRh5Ge3 structure type and their magnetic properties (R=Sm, Gd, Tb)

Powder X-ray diffraction results and macroscopic magnetic properties of new ternary RRh₅Ge₃ compounds (R=Sm, Gd, Tb) are reported. The compounds SmRh₅Ge₃ (a=2.2744(4) nm, c=0.3888(1) nm), GdRh₅Ge₃ (a=2.2711(5) nm, c=0.3872(1) nm) and TbRh₅Ge₃ (a=2.2628(7) nm, c=0.3851(1) nm) crystallize in the hexagonal SmRh₅Ge₃-type structure (space group P6₃/m; No. 176). The GdRh₅Ge₃ and TbRh₅Ge₃ compounds are Curie–Weiss paramagnets down to 5 K.     

Magnetocrystalline anisotropy and exchange interactions in the novel R3(Fe, V)29 compounds (R = Y, Nd, Sm)

A type of magnetocrystalline anisotropy and exchange interactions of the novel ternary R₃(Fe, V)₂₉ compounds (R = Y, Nd, Sm) have been investigated. The compounds are uniaxial ferromagnets with easy magnetization direction along the [ 0 1] axis of the monoclinic lattice at room temperature. The temperature variations of the magnetic moment and the first anisotropy constant for Y₃(Fe, V)₂₉ are presented. The first order magnetization process along the hard magnetization direction takes place for Sm₃(Fe, V)₂₉ at T < 120 K. A magnetic anomaly is detected in the temperature dependence of the a.c. susceptibility for Nd₃(Fe, V)₂₉ which can be related to a spin reorientation.     

Crystal structure and magnetic properties of the binary uranium–nickel alloy U11Ni16

The crystal structure of the U–Ni binary compound previously designated U₅Ni₇ was studied by X-ray single crystal diffraction showing that the exact formula is U₁₁Ni₁₆. Uranium and nickel atoms are distributed respectively on 5 and 6 Wyckoff positions of the trigonal space group R (n° 148), and the unit-cell dimensions in the hexagonal setting are: a=11.7786(4) Å, c=20.7485(8) Å. Magnetisation measurements indicate itinerant ferromagnetism below T_c=33 K for U₁₁Ni₁₆.     

Oxygen release behaviour of Ce(1−x)ZrxO2 powders and appearance of Ce(8−4y)Zr4yO(14−δ) solid solution in the ZrO2–CeO2–CeO1.5 system

To clarify the existence of metastable phases in the ZrO₂–CeO₂–CeO_1.5 system, evolved-oxygen gas analyses, (EGA), by heating a single phase of t′ and t″ (Ce_(1−x)Zr_xO₂) with various compositions, x, in a reducing gas and successive oxidation were carried out repeatedly. The oxygen release behaviour of the t′ and t″ phases was very complicated. The single κ phases, (Ce_(1−x)Zr_xO₂) with the composition, x=0.5 and 0.6, which were obtained by oxidizing the resulting pyrochlore as a precursor in O₂ gas at 873 K, exhibited a sharp oxygen release at the lowest temperature; the composition range of κ phase may be x=0.450.65. A new tetragonal phase t*, (Ce_(1−x)Zr_xO₂), which was attained by cyclic redox process together with annealing in O₂ gas at 1323 or 1423 K, exhibited a sharp oxygen release at the highest temperature; the composition range of t* phase may be as wide as x=0.200.65. A metastable solid solution expressed by a chemical formula of Ce_(8−4y)Zr_4yO_(14−δ) (y=01) possessing a CaF₂-related structure appeared on deoxidation of the t* phase. A ternary phase diagram containing the t* and Ce_(8−4y)Zr_4yO_(14−δ) solid solution was proposed.     

Magnetic properties of novel compounds R3(Fe,Cr)29Xy (R=Nd, Sm and X=N, C)

The novel ternary rare-earth iron-rich interstitial compounds R₃(Fe,Cr)₂₉X_y (R=Nd, Sm and X=N, C) with the monoclinic Nd₃(Fe,Ti)₂₉ structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV/V of about 6% and an enhancement of Curie temperatures T_c about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd₃Fe_24.5Cr_4.5X_y compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field B_cr=4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm₃Fe₂₄Cr₅X_y compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with B_cr=2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μ_OjH_c0.8 T at 293 K has been successfully developed from the Sm₃Fe₂₄Cr₅X_y (X---N and C) phases.     

Structure of Y3TaNi6+xAl26: a filled-up substitution variant of the BaHg11 type

The crystal structure of Y₃TaNi_6+xAl₂₆ (refined composition Y₄TaNi_6+[7]Al_20+[6]) was determined by single-crystal X-ray diffraction (λ(Mo K) −0.71073 A. μ −17.827 mm¹, F(000) = 700, T = 293 K, wR = 0.015 for [8] unique reflections). This new quaternary aluminide crystallizes with a cubic structure. Pearson code cP49-12.85, (221) Pm-3m-ji'gdba, a = 8.3600(1) Å. V = 584.28(2) Å, Z = 1, M₁ = 1510.25, D_x = 4.292 mg mm¹. The structure of Y_xTaNi_6+xAl₂₆ is filled-up substitution variant of the BaHg₁₁ structure type with one additional atom site, partly occupied (around 15%) by Ni atoms, located at the centre of a cube formed by Al atoms. Distinct atom coordinates were refined for Ni and Al atoms on a site for which mixed occupation (approximately 50% Ni/50% Al) was found. The Ta atoms centre regular Al atom cuboctahedra, and the Y atoms 20-vertex polyhedra, formed by Al and Ni atoms, similar to those observed in CeMn₄Al₈ and YbFe₂Al₁₀.     

The crystal structure of the novel ternary silicide Sm4Pd4Si3

The crystal structure of the compound Sm₄Pd₄Si₃ was determined by the single-crystal method (KM-4 automatic diffractometer, Mo K radiation. Sm₄Pd₄Si₄ has the monoclinic Nd₄Rh₄Ge, type structure: space C2/c, mC44 (No. 15). a = 20.693(6), B = 5.584(1), C = 7.699(2) Å, β = 109.48(3)°, V = 838 Å, Z = 4, μ - 36.23 mm¹, R =_F = 0.0537, R _F = 0.0435 for 1652 unique reflections. The coordination numbers of samarium atoms are 17 and 18. For palladium and silicon atoms icosahedra and trigonal prisms with additional atoms are typical as coordination polyhedra. The structure of Sm₄Pd₄Si₄ is composed of fragments of the YPd₂Si and Y₁Rh₂Si₂ structure in a ratio 1:1.     

Magnetic ordering in ternary RMn2Ge2 compounds (R = Tb, Ho, Er, Tm, Lu) from neutron diffraction study

The compounds RMn₂Ge₂ (R = Tb, Ho, Er, Tm, Lu) have been investigated by neutron diffraction. TbMn₂Ge₂ is a collinear ferrimagnet with the Mn and Tb moment aligned along the c axis (μ_TB = 8.81(59) μ_B: μ_Mn = 2.21(44) μ_B). HoMn₂Ge₂ exhibits incommensurale ordering below 2.1 K characterized by two wavevectors at 1.3 K: q₁ = (0.1543(4), 0.1543(4), 0) and q₂ = (0.210(1), 0.007(1), 0). The Mn sublattice remains antiferromagnetic down to 1.3 K (μ_Mn = 2.38(6) μ_B). The Er moments order ferromagnetically below 5.5 K in ErMn₂Ge₂ (μ_Mn = 6.81(31) μ_B). The moments are perpendicular to the c axis. The Mn sublattice remains antiferromagnetic down to 1.8 K (μ_Mn = 2.34(18) μ_B). The magnetic structure of TmMn₂Ge₂ is characterized by the propagation vector (0.0.1/2). the Tm moments lying in the basal plane. The ordering of the Tm moments yields a canting of the Mn moments (τ = 21(3)°); μ_Tm = 6.63(18) μ_B; μ_Mn = 2.28(27) μ_B). The antiferromagnetic structure of LuMn₂Ge₂ has been determined (μ_Mn = 2.32(14) μ_B). The evolution of the magnetic properties of the heavy rare earth compounds RMn₂Ge₂ is discussed.     

LaMg2NiH7, a novel quaternary metal hydride containing tetrahedral [NiH4] complexes and hydride anions

A new ternary compound of composition LaMg₂Ni has been found and investigated with respect to structure and hydrogenation properties. It crystallizes with the orthorhombic MgAl₂Cu type structure (space group Cmcm, a=4.2266(6), b=10.303(1), c=8.360(1) Å; V=364.0(1) ų; Z=4) and absorbs hydrogen near ambient conditions (<200 °C, <8 bar) thereby forming the quaternary metal hydride LaMg₂NiH₇. Neutron powder diffraction on the deuteride revealed a monoclinic distorted metal atom substructure (LaMg₂NiD₇: space group P2₁/c, a=13.9789(7), b=4.7026(2), c=16.0251(8) Å; β=125.240(3)°, V=860.39(8) ų; Z=8) that contains two symmetry independent tetrahedral [NiD₄]⁴⁻ complexes with Ni–D bond lengths in the range 1.49–1.64 Å, and six D⁻anions in tetrahedral metal configuration with bond distances in the ranges 1.82–2.65 Å (Mg) and 2.33–2.59 Å (La). The compound constitutes a link between metallic ‘interstitial’ hydrides and non-metallic ‘complex’ metal hydrides.     

Magnetic structure of YMn6Ge6 and room temperature magnetic structure of LuMn6Sn6 obtained from neutron diffraction study

Neutron diffraction measurements have been performed on the ternary compounds YMn₆Ge₆ and LuMn₆Sn₆ of HfFe₆Ge₆-type structure (space group, P6/mmm). This structure can be described as a filled derivative of the CoSn-B35-type structure. Each of the rare earth (R) and Mn atoms are successively distributed in alternate layers, stacked along the c axis with the sequence Mn---R---Mn---Mn---R---Mn. At 300 K, both compounds exhibit collinear antiferromagnetic arrangements and the magnetic structures consist of a stacking of ferromagnetic (001) layers of Mn with the coupling sequence Mn(+)---R---Mn(−)---Mn(−)---R---Mn(+) (μ_Mn ≈ 1.33(1)μ_B and 1.82(3)μ_B for LuMn₆Sn₆ and YMn₆Ge₆ respectively). For LuMn₆Sn₆, the magnetic moments lie in the (001) plane, while they are along the c axis in YMn₆Ge₆. At low temperature, a spin reorientation process occurs in both compounds, yielding incommensurate antiferromagnetic arrangements. For YMn₆Ge₆ (T_t ≈ 80 K), the Mn moments form a double-cone structure with a periodicity of about 105 Å (μ_Mn = 1.95(4)μ_B at 2 K), while only preliminary results are available for LuMn₆Sn₆ below about 200 K. The results are compared with those obtained on the CoSnB35-type structure binary compounds FeSn and FeGe, on one hand, and the RMn₆Sn₆ compounds, on the other hand.     

Far-infrared reflectance of β”-(BEDT-TTF)2AuBr2: Co-existence of free caniers and a single-particle gap at 2Δ = 130cm

We have measured the temperature dependence of far-infrared reflectance of β”-(BEDT-TTF)₂AuBr₂ to investigate the possibility of SDW transition. The polarized reflectance in two-dimensional BEDT-TTF layers shows a highly anisotropic feature of conduction band. Both the Ec and the Ec reflectance line-shapes, which are Drude-like at room temperature, demonstrate a clear dip below 100 cm⁻¹ even at 40 K. The frequency-dependent conductivity at 7 K indicates the presence of a single-particle gap at 2Δ = 130 cm⁻¹ assignable to the SDW nesting along c. The nesting fluctuation exists already at room temperature because of a strongly one-dimensional nature of the band dispersion.     

Magnetic structures of Zr6CoAs2-type Ho6−xErxMnBi2 solid solutions

Investigations were made by neutron diffraction on Zr₆CoAs₂-type (space group no. 189) Ho_6−xEr_xMnBi₂ solid solutions. The ferromagnetic ordering temperature decreases from Ho₆MnBi₂ (T_C = 200(6) K) to Er₆MnBi₂ (T_C = 100(4) K), whereas temperatures of ferrimagnetic (or antiferrimagnetic) ordering (T_Ferri and T_AFerri) are found to have non-monotonic dependences on the content of Er: T_Ferri = 58(4) K for Ho₆MnBi₂, T_Ferri = 162(4) K for Ho_4.5Er_1.5MnBi₂, T_Ferri = 150(4) K for Ho₃Er₃MnBi₂, T_AFerri = 78(4) K for Ho_1.5Er_4.5MnBi₂ and T_AFerri = 52(4) K for Er₆MnBi₂.

In these compounds, no local moment was detected on the manganese ion site, except for Ho_1.5Er_4.5MnBi₂ and Er₆MnBi₂ compounds. The manganese magnetic moments (μ_Mn) is 1.5μ_B and these are antiferromagnetically coupled with that of rare earth moments.     

The molybdenum diphosphate Mo1.3O(P2O7), containing Mo2 and Mo3 clusters

A novel molybdenum diphosphate, Mo_1.3O(P₂O₇), was obtained by electrochemical lithium deintercalation. The diphosphate crystallises in space group I2/a with the lattice parameters a=22.88(1), b=22.94(2), c=4.832(1) Å, γ=90.36°, Z=8. Its original framework is built up from MoO₆ octahedra, P₂O₇ groups and also from MoO₄, Mo₂O₄ and Mo₃O₈ units containing Mo₂ and Mo₃ clusters. These polyhedra delimit large octagonal and z-shaped tunnels running along c, in which the inserted cations may be located.