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1.
The nature of the magnetic ordering of Tb 4Sb 3 compound (Th 3P 4-type, cubic; cI28, space group , No. 220, a = 0.91518(7) nm) has been investigated by using the techniques of magnetization and neutron diffraction. AC and DC magnetisation measurements indicate antiferromagnetic ordering at 108 K in zero magnetic field that is accompanied by a field-induced metamagnetic transition to a ferromagnetic state, in fields above 0.3 T. Neutron diffraction experiment in zero applied magnetic field shows that below TN = 112(4) K Tb 4Sb 3 exhibits an antiferromagnetic flat spiral-type ordering with propagation vector K 1 = [±1/8, ±1/8, ±1/8]. The magnetic moment of Tb atoms is found to be MTb = 6.7(3) μ B at 80 K. The magnetic moment of Tb atoms lie in the (1 1 1) plane of Tb 4Sb 3 unit cell (the cone axis arranges along [1 1 1] direction with cone angle β = 90°). Below TN2 50 K, Tb 4Sb 3 shows second antiferromagnetic transition with K 2 = [1/2, 1/2, 1/2] with possible re-orientation of Tb magnetic moments. 相似文献
2.
A neutron diffraction investigation has been carried out on the trigonal La 2O 3-type ( hP5, space group , No. 164; also CaAl 2Si 2-type) YbMn 2Sb 2 intermetallic. A two-step synthesis route has been tried in this work, and successfully utilised to prepare single phase samples of this compound. This study shows that YbMn 2Sb 2 presents antiferromagnetic ordering below 120 K. The magnetic structure of this intermetallic consists of antiferromagnetically coupled magnetic moments of the manganese atoms, in the Mn1 (1/3, 2/3, ZMn) and Mn2 (2/3, 1/3, 1 − ZMn) sites; the direction of magnetic moments of manganese atoms forming a φ and a θ angle, respectively with the X- and the Z-axis. At 4 K the magnetic moment of the Mn1 atom is μMn = 3.6(1) μB, with φ = 0° and θ = 62(4)°, whilst the Mn2 atom has a magnetic moment μMn = 3.6(1) μB, with φ = 0° and θ = 242(4)°. On the other hand, in this compound no local moment was detected on the Yb site. 相似文献
3.
Investigations were made by neutron diffraction on Zr 6CoAs 2-type (space group no. 189) Ho 6−xEr xMnBi 2 solid solutions. The ferromagnetic ordering temperature decreases from Ho 6MnBi 2 ( TC = 200(6) K) to Er 6MnBi 2 ( TC = 100(4) K), whereas temperatures of ferrimagnetic (or antiferrimagnetic) ordering ( TFerri and TAFerri) are found to have non-monotonic dependences on the content of Er: TFerri = 58(4) K for Ho 6MnBi 2, TFerri = 162(4) K for Ho 4.5Er 1.5MnBi 2, TFerri = 150(4) K for Ho 3Er 3MnBi 2, TAFerri = 78(4) K for Ho 1.5Er 4.5MnBi 2 and TAFerri = 52(4) K for Er 6MnBi 2. In these compounds, no local moment was detected on the manganese ion site, except for Ho1.5Er4.5MnBi2 and Er6MnBi2 compounds. The manganese magnetic moments (μMn) is 1.5μB and these are antiferromagnetically coupled with that of rare earth moments. 相似文献
4.
The new ternary compound Dy 1.2Fe 4Si 9.8 have been prepared and studied by means of X-ray powder diffraction technique and vibrating sample magnetometer. The ternary compound Dy 1.2Fe 4Si 9.8 crystallizes in the hexagonal Er 1.2Fe 4Si 9.8-type structure, space group P6 3/ mmc (no. 194) with lattice parameters a = 0.39415(1) nm and c = 1.52771(3) nm. The crystal structural refinement of the compound Dy 1.2Fe 4Si 9.8 has been performed by using Rietveld method. Lattice thermal expansion studies on the compound were carried out in the temperature range from 298 to 1013 K. The variation of the unit cell parameters shows that the unit cell parameters increase with the increase in temperature. The coefficients of average lattice thermal expansion along various axes in the temperature range from 298 to 1013 K are , and . The temperature dependence of the magnetization for the compound was also investigated in the range from 90 to 300 K. The experimentally determined magnetic effective paramagnetic moment is μeff = 11.3 μB per formula unit (10.3 μB per Dy atom). 相似文献
5.
A new ternary compound Ce(Au,Sb) 2, with a homogeneity range has been observed from X-ray powder diffraction of as cast alloys, a = 4.743–4.712 Å, c = 3.567–3.768 Å. Its crystal structure was investigated by X-ray diffraction from Ce(Au 1−xSb x) 2 ( x = 0.266) single crystal: CAD-4 automatic diffractometer, Mo K radiation, a = 4.7256(6) Å, c = 3.6711(6) Å, P6/ mmm space group, V = 70.997(17) Å 3, Z = 1, ρ = 10.732 Mg/m 3, μ = 76.369 mm −1, R1 = 0.0415, wR2 = 0.0793 for 99 reflections with I > 2 σ( I0). The coordination polyhedron of X (X = 0.734Au + 0.266Sb) atom is a full-capped trigonal prism [XCe 6X 3X 2]. Ce atom is coordinated by 14 atoms: [CeX 12Ce 2]. The compound is isotypic with UHg 2 structure, a deformation derivative of AlB 2 structure type. It forms isostructural compounds with La and Pr. 相似文献
6.
Two polymorphs (I and II) of Ba 3Sn 2P 4 have been found in the same preparative batch. Both compounds crystallize in the centrosymmetric monoclinic space group P2 1/ c (#14, a = 7.8669(2) Å, b = 19.2378(5) Å, c = 7.8472(2) Å, β = 112.77(1)°, V = 1095.06(5) Å 3, Z = 4, and R/ wR = 0.0303/0.0710 for I; a = 7.8771(3) Å, b = 19.4099(7) Å, c = 7.7040(3) Å, β = 112.44(1)°, V = 1088.67(7) Å 3, Z = 4, and R/ wR = 0.0224/0.0415 for II). Both structures consist of one-dimensional chains separated by Ba 2+ cations. The isolated chain consists of condensed ethane-like [Sn 2P 6] units. In polymorphs I and II, the condensation and connectivity of the [Sn 2P 6] units are quite different. While [Sn 2P 6] units form four- and six-membered rings in I, they form the five-membered rings in II. The electronic structure calculations indicate that semiconducting behavior is expected for both compounds. 相似文献
7.
The structure, magnetization and magnetostriction of Laves phase compound TbCo 2 are investigated by temperature dependent high resolution neutron powder diffraction. The compound crystallizes in the cubic Laves phase C15 structure above its Curie temperature TC and exhibits a rhombohedral distortion (space group ) below TC. By an appropriate extrapolation of the temperature factor of Co atom above TC, the Rietveld refinement of the neutron powder diffraction data of the rhombohedral structure converges satisfactorily and reveals that the moments of Co1(3b) and Co2(9e) are almost equal. Tb moment follows well the Brillouin function. The total magnetic moment of TbCo 2 is about 5.8 μB/f.u., the anisotropic magnetostriction constant λ111 is about 4.6 × 10 −3 and the volume magnetostriction ωs is about 8.7 × 10 −3 at 14 K. 相似文献
8.
A new mixed-valence iron phosphate Na 1.25Mg 1.10Fe 1.90(PO 4) 3 has been synthesized as single crystals by a flux technique and its structure has been refined from X-ray data to a residual R1 = 0.032. The compound crystallizes in the monoclinic space group C2/ c with the parameters: a = 11.7831(3) Å, b = 12.4740(3) Å, c = 6.3761(2) Å, β = 113.643(2)° and Z = 4. The structure belongs to the alluaudite structural type, and thus it obeys to the X(2)X(1)M(1)M(2) 2(PO 4) 3 general formula. The X(2) and X(1) sites are occupied by sodium while the M(1) and M(2) sites feature a statistical distribution of iron and magnesium. Additional information about the cation distribution has been extracted from a Mössbauer spectroscopy study which confirmed the mixed valency of the compound. A magnetic susceptibility study has also been undertaken and has shown the compound to be antiferromagnetic with a Neel temperature of about 35 K. 相似文献
9.
The crystal structures of the Ag 4HgGe 2S 7 and Ag 4CdGe 2S 7 compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.74546(8), b=0.68093(2), c=1.05342(3) nm, β=93.398(3)° for Ag 4HgGe 2S 7 and a=1.74364(8), b=0.68334(3), c=1.05350(4) nm, β=93.589(3)° for Ag 4CdGe 2S 7. Atomic parameters were refined in the isotropic approximation ( RI=0.0761 and RI=0.0727, respectively). 相似文献
10.
The relationship between the electronic and molecular structure has been established based on the complete energy matrices for a 3d 5 configuration ion in a tetragonal ligand-field. By diagonalizing the complete energy matrices, the zero-field splitting parameters and the local lattice structure of the tetragonal FeF 5O cluster in KMgF 3:Fe 3+ crystal have been studied. The distortion of local lattice distortion structure parameters Δ R1 = 0.10464 Å and Δ R2 = 0.10094 Å are determined. Simultaneously, the local lattice structure parameters R1 = 1.88936 Å and R2 = 1.89306 Å, which reflect the interactions between impurity and crystal lattice, are determined from our calculation. 相似文献
11.
The subsolidus phase relationships of ternary system Na 2O–ZnO–WO 3 have been investigated by X-ray diffraction (XRD) and differential thermal analyzer (DTA). All the samples were synthesized in the temperature range from 530 to 850 °C in air. There are one ternary compound and five binary compounds in the Na 2O–ZnO–WO 3 system, which can be divided into eight three-phase regions. The crystal structure of the ternary compound Na 3.6Zn 1.2(WO 4) 3 is determined by single-crystal structure analysis method. It belongs to triclinic system with space group and lattice constants a = 7.237 (5) Å, b = 9.172 (6) Å, c = 9.339 (6) Å and = 94.920 (4)°, β = 105.772 (9)°, γ = 103.531 (8)°, Z = 2. DTA analyses indicate that the compound Na 2WO 4 is not suitable to be the flux for ZnO crystal growth below 1250 °C, since no liquidus was observed in the system before 1250 °C. 相似文献
12.
The polarized absorption and emission spectra have been measured for the Tm 3+ doped NaY(MoO 4) 2 crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters ( t = 2, 4, 6) are 11.67 ×10 −20, 2.21 × 10 −20, 1.74 × 10 −20 cm 2, respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm 3+ doped laser crystals, Tm 3+:NaY(MoO 4) 2 crystal has potential as a promising laser crystal. 相似文献
13.
Crystalline ruthenium dioxide (RuO 2) has been ball-milled in an O 2 atmosphere and the changes in the physico-chemical properties induced by different milling atmospheres (Ar and O 2) or milling sequences have been established. Cyclic voltammetry and BET measurements were used to evaluate the electrochemically active surface charge ( , expressed in C g −1) and the specific surface area (expressed in m 2 g −1), respectively. The extent of oxygen uptake in the processed samples was determined by X-ray photoelectron spectroscopy (XPS). The value of RuO 2 milled under O 2 for 30 h (sample S4) is 120.7 C g −1, a factor of two higher than the value of RuO 2 milled under Ar for the same period of time (sample S1, 60.3 C g −1). A still higher value is obtained when the O 2 atmosphere of the crucible is frequently replenished (sample S5, 138.7 C g −1) or when the milling operation is prolonged up to 81 h (sample S6, 160.5 C g −1). These changes are paralleled by a variation of the BET surface area, which increases from 24 m 2 g −1 for sample S1 to 51.5 m 2 g −1 for sample S5. The concentration ratio [O bound to Ru]/[Ru] determined by XPS increases steadily from sample S1 to sample S6, indicating that the amount [O bound to Ru] increases with the exposure of RuO 2 to oxygen during the milling process. All these changes are explained by the fact that freshly exposed RuO 2 surfaces created during the milling process react with O 2 molecules, thereby lowering the surface energies and the tendency of the milled material to cluster into larger aggregates. 相似文献
14.
Magnetoelectric composites, namely xNiFe 2O 4 + (1 − x)Ba 0.8Sr 0.2TiO 3 were prepared by standard double sintering ceramic method. The X-ray diffraction measurements were carried out to check the phase purity and to calculate the lattice constants. scanning electron microscopy (SEM) micrographs were taken to understand the microstructure of the samples. Dielectric property such as dielectric constant ( ε′) was also studied as a function of frequency in the range 100 Hz–1 MHz. The ac conductivity as a function of frequency and dc resistivity as a function of temperature were studied for different compositions. The hysteresis measurements were done to determine saturation magnetization ( Ms) and coersivity ( Hc) and magnetic moment was calculated. Effect of resistivity on ME voltage coefficient is studied. 相似文献
15.
The crystal and magnetic structures of the Laves phase compound NdCo 2 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 TC (≈100 K), in space group I4 1/ amd below TC and in space group Imma below the tetragonal–orthorhombic structural/magnetic transitions at TM ≈ 42 K. The assignment of the space groups to the crystal structures of NdCo 2 in different temperature ranges complies with the reported Mössbauer studies. Detailed information of the crystal and magnetic structures of NdCo 2 at different temperatures are reported. 相似文献
16.
Co/Co 3O 4 bilayer films were fabricated by RF sputtering with Co and Co 3O 4 targets. Exchange bias effect in the bilayer films was observed at 80 K by vibrating sample magnetometer. The bias effect disappeared about 240 K slightly lower than the Néel point of CoO and much higher than the Néel temperature of Co 3O 4 about 40 K. To clarify the origin of the exchange bias effect, Auger and X-ray photoelectron spectroscopy were employed and CoO was found at a transition region from Co 3O 4 layer to Co layer due to oxygen diffusion during sputtering. The angular dependence of exchange bias field HE was obtained to obey function of HE(θ)=18.06 (kA/m)[−cos θ+0.22 cos 3θ+0.03 cos 5θ−0.01 cos 7θ+]. 相似文献
17.
The crystal structure of the monoclinic phase η-Al 11Cr 2 of the space group C2/ c, a ≈ 1.76 nm, b ≈ 3.05 nm, c ≈ 1.76 nm, β ≈ 90° [L.A. Bendersky, R.S. Roth, J.T. Ramon, D. Shechtman, Metall. Trans. A 22A (1991) 5] has been determined by single-crystal X-ray diffraction. The structure model, refined to a final R value of 0.0441, has the composition of Al 83.8Cr 16.2. a = 1.77348(10) nm, b = 3.04555(17) nm, c = 1.77344(10) nm, monoclinic angle β = 91.0520(12)°. There are 80 (66Al + 14Cr) independent atomic positions in a unit cell, of which all Cr atom sites and 8 Al atom sites have icosahedral coordination. These icosahedra are interconnected forming icosahedral chains along , (1 0 1) icosahedral layer blocks as well as a three-dimensional icosahedral structure. 相似文献
18.
A new compound CePt 2+xSb 2−y ( x = 0.125, y = 0.25) was synthesized by arc-melting of the elements. The chemical and structural characterizations were carried out at room temperature on as-cast samples using X-ray diffractometry, metallographic analysis and EDS-microanalysis. According to the results of X-ray single crystal diffraction this antimonide crystallizes in I4 cm space group (no. 108), Z = 32, ρ = 12.19 Mg/m 3, μ = 89.05 mm −1 ( a = 12.5386(3) Å, c = 21.4692(6) Å (crystal I) and a = 12.5455(2) Å, c = 21.4791(5) Å (crystal II)). The structure and composition were confirmed by powder X-ray diffraction ( a = 12.4901(2) Å, c = 21.3620(4) Å) and EDS-microanalysis respectively. Isotypic compounds were observed with La and Pr from X-ray powder diffraction of as-cast alloys at room temperature ( a = 12.6266(4) Å, c = 21.4589(6) Å for LaPt 2+xSb 2−y and a = 12.5184(5) Å, c = 21.4178(7) Å for PrPt 2+xSb 2−y). The CePt 2+xSb 2−y structure is derived from CaBe 2Ge 2 ( a = 2 a0 − 2 b0, b = 2 a0 + 2 b0, c = 2 c0) and comprises a new atomic arrangement with both vacancy on 4(b) pyramidal site and substitution of antimony atoms (X) by platinum (B) in the B–XX–B layers (referring to the subcell structure) forming two B––1/2B1/2XX–3/4B and two X–BB–X layers per cell. The structure of CePt 2+xSb 2−y is compared with those reported before for URh 1.6As 1.9 and CeNi 1.91As 1.94. 相似文献
19.
The crystal structure of intermetallic compound Gd 6Cr 4Al 43 has been investigated by means of X-ray diffraction data (Ho 6Mo 4Al 43 structure type, space group P6 3/ mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å). SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at TN1 = 19.0(1) K and TN2 = 6.8(1) K, respectively. 相似文献
20.
The structure and anelastic properties of Fe-27 at.%Ge alloy are studied. Long-term annealing of the as-cast alloy at 1273 K leads to homogenising and several transformations take place below 873 K. These low temperature transitions are studied by several methods: X-ray diffraction, calorimetry, vibrating-sample magnetometry and internal friction, and are related to magnetic transitions in the different phases. A high stability of the hexagonal (D0 19) phase at room temperature is recorded. The hexagonal β (B8 1) phase is also detected in the alloy at room temperature, while the presence of the ′ and phases is doubtful. A broad internal friction relaxation peak with the relaxation strength of Δ = 0.0036, the activation energy of about 1.78 eV and the preexponential relaxation time of τ0 = 2 × 10 −17 s was discovered and classified as the Zener peak in both the and β phases. 相似文献
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