Isothermal section at 950 °C of the U–Fe–B ternary system

A systematic investigation of the isothermal section at 950 °C of the U–Fe–B ternary system was done by means of X-ray powder diffraction, scanning electron microscopy, complemented by energy dispersive X-ray spectroscopy, and electron-probe microanalysis. At this temperature the phase diagram is characterized by the formation of four ternary compounds with negligible homogeneity regions. The compounds are: UFeB₄ (orthorhombic YCrB₄-type structure, a = 5.887(1) Å, b = 11.412(2) Å and c = 3.4355(4) Å), UFe₃B₂ (hexagonal CeCo₃B₂-type structure, a = 5.049(1) Å and c = 2.9996(7) Å), ∼UFe₄B (structure closely related with the CeCo₄B-type, and a small hexagonal cell a = 4.932(1) Å and c = 7.037(2) Å), and U₂Fe₂₁B₆ (Cr₂₃C₆-type structure, a = 10.766(4) Å).     

Crystal structure and properties of U2Co3Al9

A new ternary compound with stoichiometry U₂Co₃Al₉ has been synthesized. It adopts the orthorhombic Y₂Co₃Ga₉-type structure (space group Cmcm, Z = 4, a = 12.824(2) Å, b = 7.515(1) Å, c = 9.249(2) Å). Measurements of dc- and ac-magnetic susceptibility, electrical resistivity, and magnetoresistivity on polycrystalline samples have been performed. The Curie–Weiss law is strictly followed, with θ_CW = −48 K and μ_eff = 3.2 μ_B. A small kink observed in the temperature dependence of the resistivity is attributed to a phase transition at T_t = 8 K. The magnetoresistivity was found to be negative at all temperatures examined below 45 K, with a sharp minimum at T_t = 8 K.     

High-temperature thermoelectric properties of Sr2RuYO6 and Sr2RuErO6 double perovskites influenced by structure and microstructure

The high-temperature thermoelectric properties of Sr₂RuYO₆ and Sr₂RuErO₆ double perovskites were evaluated and reported for the first time. These compounds show high Seebeck coefficients not only at room temperature, but also at high temperature (for Sr₂RuYO₆, S_RT ≈ ?475 μV K^?1 and S_1200K ≈ ?250 μV K^?1; Sr₂RuErO₆, S_RT ≈ ?400 μV K^?1 and S_1200K ≈ ?250 μV K^?1). The n-type semiconducting behaviour dominates the resistivity values. Both compounds crystallize in a monoclinic unit cell (space group P2₁/n). The lattice parameters are a = 5.7761(2), b = 5.7804(1), c = 8.1689(1), α = γ = 90° and β = 90.2087(8)° for the Sr₂RuYO₆, and a = 5.7760(1), b = 5.7722(0), c = 8.1544(4), α = γ = 90° and β = 90.2099(7)° for Sr₂RuErO₆. The unit cell can be described approximately as √2a_p × √2a_p × 2a_p, where a_p is the unit cell parameter of the ideal cubic perovskite structure. High-resolution transmission electron microscopy shows an interesting three-dimensional micro-twin-domain texture where the c axis is placed in the three space directions. Structural transitions at high temperatures (T_t(Sr₂RuYO₆) ≈920 K and T_t(Sr₂RuErO₆) ≈890 K) are observed by specific heat measurement in both compounds, which are found to have a strong influence on the Seebeck coefficient and electrical conductivity.     

Intermetallic compounds in the M–Cu–Sn systems with M = Eu,Sr, Ba

Several samples were prepared in the title systems, starting from the elements sealed under argon in Ta crucibles, melting in an induction fornace and annealing at 823 K. Six ternary phases were found: EuCu₂Sn₂, a = 11.100 (3), b = 4.307 (1), c = 4.824 (1) Å, β = 108.88 (1)°, and SrCu₂Sn₂, a = 11.197 (4), b = 4.322 (2), c = 4.859 (1) Å, β = 108.43 (1)°, C2/m, CaCu₂Sn₂-type, closely related to the BaAl₄ structure; Sr₃Cu₈Sn₄, a = 9.3280 (2), c = 7.8826 (4) Å, P6₃mc, Nd₃Co₈Sn₄-type, ordered variant of the BaLi₄-type; SrCu₄Sn₂, a = 8.176 (1), c = 7.799 (1) Å, I4/mcm, CaNi₄Sn₂-type; SrCu₉Sn₄, a = 8.663 (1), c = 12.457 (2) Å, and BaCu₉Sn₄, a = 8.717 (1), c = 12.545 (2) Å, I4/mcm, LaFe₉Si₄-type, ordered variant of the NaZn₁₃ structure. The structure of the first compound was refined by the Rietveld method, while single crystal data were used for the others. Some remarks are given on the crystal chemistry of the encountered and related structure types.     

Crystal structure and properties of the new ternary compound Mg21Ga5Hg3

The crystal structure of a new ternary compound Mg₂₁Ga₅Hg₃ has been studied using X-ray powder diffraction data by Rietveld method. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for sample composition examination. The compound crystallizes in the Ge₈Pd₂₁ structure type (space group I4₁/a, a = 1.45391(5) nm, c = 1.15955(4) nm, Z = 4). All interatomic distances indicate metallic type bonding. The average thermal expansion coefficients α_a, α_c and α_V of Mg₂₁Ga₅Hg₃ are 2.60 × 10^?5 K^?1, 2.02 × 10^?5 K^?1, and 7.25 × 10^?5 K^?1, respectively. Electrical resistivity of Mg₂₁Ga₅Hg₃ was measured between 5 and 300 K.     

Magnetic and structural properties of BaFe12−xGaxO19 nanoparticles

The structural and magnetic properties of barium hexaferrite nanoparticles (BaFe_12?xGa_xO₁₉) with x = 0.0–1.0, prepared by ball milling were investigated using XRD, TEM, and VSM. It was found that the particles and crystallites have similar mean size of ～41 nm for all investigated samples. The saturation magnetization decreased slightly and nonlinearly with increasing x, and this was attributed to different preferential site occupation of Ga at low and high concentration ranges. The coercivity decreased slightly with increasing x for low concentrations of Ga (x ≤ 0.2), and then increased with increasing Ga concentration up to x = 1.0. This behavior of the coercivity was attributed to the change in the exchange coupling, which was confirmed by the variation of SFD, remanence ratio and Curie temperature with Ga concentration in the samples.     

Spin-glass-like behaviour in the ternary U3Fe4+xAl12−x uranium–iron aluminide

The U₃Fe_4+xAl_12?x (0 < x < 0.5) intermetallic was prepared by arc melting, followed by annealing at 850 °C. This compound crystallizes in the hexagonal Gd₃Ru₄Al₁₂-type structure (e.g. P6₃/mmc), with room temperature parameters a = 8.7516(3) Å and c = 9.2653(4) Å for x = 0. The structure is characterized by planar layers of M3Al4 (M = Gd, U), containing M atoms in a triangular arrangement and forming a distorted Kagomé net. Magnetic measurements revealed a spin-glass-type behaviour with a freezing temperature, T_f = 7.9 K. The magnitude of the frequency shift of the freezing temperature is ≈0.03 and a Vogel–Fulcher law is followed with values typical for a spin-glass. ⁵⁷Fe Mössbauer data show that there is no freezing of the iron magnetic moments directions below T_f, indicating that the origin of the spin-glass-like behaviour is related to topological frustration of the uranium moments.     

Magnetic ordering of novel La3NiGe2-type R3CoGe2 compounds (R = Pr,Nd, Sm,Gd–Dy)

The novel R₃CoGe₂ compounds adopt the La₃NiGe₂-type structure (space group Pnma) with the following cell parameters: a = 1.1706(1), b = 0.42267(5), c = 1.1242(1) nm for Sm₃CoGe₂; a = 1.15845(5), b = 0.41905(2), c = 1.12088(5) nm for Gd₃CoGe₂; a = 1.14942(4), b = 0.41705(2), c = 1.11030(4) nm for Tb₃CoGe₂ and a = 1.1431(2), b = 0.41500(5), c = 1.1040(2) nm for Dy₃CoGe₂. The R₃CoGe₂ compounds undergo a ferrimagnetic type ordering (T_CN = 150 K for Gd₃CoGe₂). Neutron diffraction studies show that Pr₃CoGe₂ and Nd₃CoGe₂ have a commensurate ferromagnetic component along the a axis and a commensurate antiferromagnetic component along the c axis (Pn’ma magnetic space group): (M_Pr^F)_a = 2.59(9) μ_B, (M_Pr^AF)_c = 1.58(4) μ_B, ∣M_Pr∣ = 3.03(9) μ_B for Pr₃CoGe² and (M_Nd^F)_a = 2.6(1) μ_B, (M_Nd^AF)_c = 1.65(6) μ_B, ∣M_Nd∣ = 3.1(1) μ_B for Nd₃CoGe₂ at 2 K.Magnetocaloric effect of Gd₃CoGe₂ in terms of the isotherm entropy change, ΔS_iso, was derived from the magnetization measurement, and it reaches the maximum value of ΔS_iso = ?4.9 J/kg?K in the 139–144 K temperature range.     

On new ternary phases from Eu–Zn–T (T = Al and Ga) systems

Novel ternary phases EuZn_2?xGa_2+x, EuZn_2?xAl_2+x, Eu₂Zn_14.32Al_2.68 and Eu₃Zn_17.68Al_4.32 have been synthesized at 400 °C, and characterized by means of X-ray single crystal diffraction at room temperature and magnetic measurements down to 1.72 K. EuZn_2?xAl_2+x and EuZn_2?xGa_2+x compounds crystallize with tetragonal unit cells of the BaAl₄-type. Representatives of these series, namely EuZn_1.25Al_2.75 and EuZnGa₃, order ferromagnetically below 25 K and 14 K, respectively, due to the presence of divalent Eu ions. The other two ternaries studied, i.e. Eu₂Zn_14.32Al_2.68 and Eu₃Zn_17.68Al_4.32, adopt the rhombohedral Th₂Zn₁₇- and the tetragonal Ce₃Zn₂₂-type structure, respectively. Both compounds form with Eu²⁺ ions and possibly order antiferromagnetically at the lowest temperatures investigated.     

Enhancement of glass-forming ability of FeGaPCB bulk glassy alloy with high saturation magnetization

The effect of Mo and Si additions on the glass-forming ability (GFA) of Fe–Mo–Ga–P–C–B–Si alloys was investigated. The addition of 2 at% Mo combined with 2 at% Si was found to be effective for the extension of the supercooled liquid region (ΔT_x) defined by the difference between glass transition temperature (T_g) and crystallization temperature (T_x). The ΔT_x value is 26 K for the Fe₇₈Ga₂P₁₂C₄B₄ alloy, and increases to 52 K for the Fe₇₆Mo₂Ga₂P₁₀C₄B₄Si₂ glassy alloy. In addition, this glassy alloy exhibits a highly reduced glass transition temperature (T_g/T_l) of 0.59. Large ΔT_x and high T_g/T_l enabled us to prepare the Fe₇₆Mo₂Ga₂P₁₀C₄B₄Si₂ bulk glassy alloy successfully with a diameter of 2 mm and with a high saturation magnetization (I_s) of 1.32 T. The Fe₇₆Mo₂Ga₂P₁₀C₄B₄Si₂ glassy alloy also exhibits good soft magnetic properties, i.e., high effective permeability at 1 kHz of 9700 and low coercive force of 3 A/m.     

Crystal and electronic structures and physical properties of two semiconductors: Pb4Sb6Se13 and Pb6Sb6Se17

The title compounds were synthesized by directly reacting the elements in stoichiometric ratios at elevated temperatures. Their crystal structures were determined by single crystal X-ray diffraction. Pb₄Sb₆Se₁₃ crystallizes in the monoclinic space group I2/m with lattice dimensions of a=24.591(1) Å, b=4.0910(2) Å, c=25.212(1) Å, β=93.943(1)°, V=2530.3(2) Å³ (Z=4), while Pb₆Sb₆Se₁₇ crystallizes in the orthorhombic space group P2₁2₁2 with lattice dimensions of a=15.872(4) Å, b=24.061(7) Å, c=4.1382(9) Å, V=1580.4(7) Å³ (Z=2). Electronic structure calculations predicted semiconducting behavior. Temperature dependent electrical conductivity measurements verified this prediction for Pb₄Sb₆Se₁₃.     

Crystal structure of the new ternary germanide Tb4Zn5Ge6

The Tb₄Zn₅Ge₆ phase was prepared by arc melting in an argon atmosphere and then annealed at 670 K for 400 h. The structure of orthorhombic Tb₄Zn₅Ge₆ was determined by single-crystal X-ray diffraction (Cmc2₁, Z = 4, a = 4.2330(10) Å, b = 18.576(4) Å, c = 15.275(3) Å, R₁ = 0.0272 and wR₂ = 0.1076). The structure is isostructural to Gd₄Zn₅Ge₆ and composed of edge- and corner-sharing ZnGe₄ tetrahedra, Tb-atoms forms trigonal prisms filled by Ge-atom.     

Martensitic transformation and magnetic properties in Ni–Fe–Ga–Co magnetic shape memory alloys

Ni–Fe–Ga–Co is a promising system for magnetic shape memory alloy applications, due to its good ductility, mobile twin boundaries and high transformation temperatures. Unlike previous studies which focused on compositions with a Ga content of 27 at.%, here the martensitic transformation and magnetic properties over a large composition range of Ni_54−xFe₂₀Ga₂₆Co_x, Ni_54−xFe₁₉Ga₂₇Co_x, Ni_56−xFe₁₇Ga₂₇Co_x and Ni_54−xFe₁₈Ga₂₈Co_x (x = 0, 2, 4) are investigated. The martensitic transformation temperature T_m and the Curie temperature T_c can be tailored in a wide range by changing composition and heat treatment. A coupling of martensitic and magnetic transformations at ∼90 °C is found for Ni₅₂Fe₁₇Ga₂₇Co₄. Additionally, the effect of thermal cycling on the martensitic transformation of single- and two-phase Ni–Fe–Ga–Co alloys is discussed. Furthermore, an intermediate face-centered cubic phase induced by powderization and transformed into a body-centered cubic phase by aging is reported. The saturation magnetization is significantly decreased by powderization, while recovered by the subsequent aging.     

One-dimensional antiferromagnetic behavior of a chiral molecular crystal, α′-(S,S-DMBEDT-TTF)2PF6

The synthesis, crystal and electronic structures, resistivity, magnetic susceptibility, and dielectric constant of the novel chiral crystal, α′-(S,S-DMBEDT-TTF)₂PF₆ [DMBEDT-TTF = dimethylbis(ethylenedithio)tetrathiafulvalene] are presented. The α′-type donor arrangement affords the one-dimensional antiferromagnetic behavior with J = ?40 K. The calculated band structure indicates the pseudo-one-dimensional interaction in the molecular side-by-side direction along the b-axis. The frequency-dependent dielectric constant suggests the charge disproportionation above 100 K. The non-centrosymmetric space group due to the composed chiral molecules affords the possibility of piezoelectricity.     

The effect of Co doping on the magnetic entropy changes in Ni44−xCoxMn45Sn11 alloys

A series of Ni_44?xCo_xMn₄₅Sn₁₁ (x = 0, 1, and 2) ferromagnetic shape memory alloys (FSMAs) were prepared by arc melting method. The martensitic transition (MT) and Curie temperatures vary obviously with Co addition. With the increasing temperature, the magnetization increases from a weak-magnetic martensite to a ferromagnetic austenite, for x = 0 and 1. But in the case of x = 2, the magnetization increases from a ferromagnetic martensite to another ferromagnetic austenite. Under an applied magnetic field of 10 kOe, the peak values of magnetic entropy changes are 10.1, 14.1, and 6.2 J/(kg K), for x = 0, 1, and 2, respectively. The magnetic phase transition near the martensitic transition temperatures and the field-induced metamagnetism should account for the large magnetic entropy changes.     

Ternary phases in the Yb–Zn–Al system with La3Al11- and Yb8Cu17Al49-type structures

Several compounds with La₃Al₁₁- and Yb₈Cu₁₇Al₄₉-type structures were synthesized in the ternary Yb–Zn–Al system and their crystal structure and existence range were determined by both single-crystal and powder methods. For two of them, crystallizing with the La₃Al₁₁-type, orthorhombic, Immm, o/28, refinement was made by single-crystal data: Yb₃Zn_6.16Al_4.84, a = 428.95(4) pm, b = 975.5(1) pm, c = 1257.3(2) pm, wR2 = 0.052; Yb₃Zn_4.84Al_6.16, a = 427.03(5) pm, b = 988.6(1) pm, c = 1249.5(2) pm, wR2 = 0.104. Though zinc and aluminium share the same sites, some preferential occupation is recognizable. This phase forms between 35 and 50 at% Al. On the Zn-rich side, starting from binary Yb₃Zn₁₁, a replacement of ∼3 at% Al for Zn is reached, then a heterogeneity range appears. Two other phases, crystallizing with the Yb₈Cu₁₇Al₄₉-type, tetragonal, I4/mmm, tI74, were determined by single-crystal methods: Yb₈Zn_48.5Al_17.5, a = 874.6(2) pm, c = 1615.8(3) pm, wR2 = 0.055; Yb₈Zn_41.4Al_24.6, a = 869.5(3) pm, c = 1637.1(7) pm, wR2 = 0.104. The structure of these latter compounds can be related to the Th₆Mn₂₃ type. A common building unit is found and several coordination polyhedra show similar features. Two atomic sites with zinc only and four with Zn/Al mixtures are filled.     

Glass-forming ability and soft magnetic properties of (Co0.6Fe0.3Ni0.1)67B22+xSi6−xNb5 bulk glassy alloys

The glass-forming ability (GFA) and soft-magnetic properties of (Co_0.6Fe_0.3Ni_0.1)₆₇B_22+xSi_6?xNb₅ (x = 0–1.5) bulk glassy alloys was investigated. The DSC curves show that the (Co_0.6Fe_0.3Ni_0.1)₆₇B_22+xSi_6?xNb₅ bulk glassy alloys have a wide supercooled liquid region (ΔT_x) of about 60 K, and high reduced glass transition temperature (T_g/T_l) lies in the range from 0.628 to 0.649. By copper mold casting method, the bulk glassy alloys with diameters up to 4.5 mm can be formed. In addition to high GFA, the Co-based bulk glassy alloys also exhibit good soft-magnetic properties, i.e., saturation magnetization of 0.58–0.61 T, low coercive force of 0.83–1.46 A/m, and high permeability of (1.79–2.2) × 10⁴ at 1 kHz under a field of 1 A/m. These Co-based bulk glassy alloys are promising for future applications as a new structural and functional material.     

High-temperature ferromagnetism observed in facing-target reactive sputtered MnxTi1−xO2 films

The crystal structure of reactive sputtered Mn_xTi_1−xO₂ films turns from anatase to rutile as x increases. All the films are ferromagnetic, with a Curie temperature above 340 K. Vacuum annealing enhances the ferromagnetism of the films, but O₂ annealing weakens it, indicating that the ferromagnetism is related to the oxygen-vacancy defects created by Mn⁺² dopants at Ti⁺⁴ cations. The average room-temperature moment per Mn decreases from 0.482 μ_B at x = 0.026 to 0.078 μ_B at x = 0.375. Meanwhile, the optical band gaps value decreases linearly from 3.35 eV at x = 0 to 1.73 eV at x = 0.375, suggesting that Mn ions substitute for Ti ions uniformly and the ferromagnetism is not from magnetic Mn oxide impurities. The high-temperature ferromagnetism makes the Mn_xTi_1−xO₂ films useful for the applications in spintronic devices.     

Structural and magnetic properties of PrFe12−xVx and their nitrides

The structural and magnetic properties of novel permanent magnet materials, PrFe_12−xV_xN_y (x=1.25∼2.0; y≈1.6), have been studied systematically. It is shown that the nitrides crystallize in the same ThMn₁₂-type structure as the parent alloys, with the unit cell volume expansion upon nitrogenation. Neutron diffraction performed on PrFe_10.5V_1.5N_0.4 at room temperature reveals that the vanadium atoms occupy the 8i sites, while the nitrogen atoms occupy the 2b sites and the iron atoms occupy the 8j, 8f and the rest 8i sites in the ThMn₁₂-type structure. Typical interstitial modification effects are observed in PrFe_12−xV_xN_1.6. The Curie temperature is raised to as high as 800 K and the saturation magnetization is increased to 1.54 T at room temperature. Mossbauer spectra studies also show that the hyperfine field and isomer shift are strongly enhanced upon nitrogenation. Nitrogenation changes the easy magnetization direction from the ab-plane to the c-axis with an anisotropy field up to 10.5 MA/m (132 kOe). Crystal field coefficients for Pr³⁺ in PrFe_12−xV_x and PrFe_12−xV_xN are calculated to explain this change in magnetocrystalline anisotropy behaviors. As a preliminary attempt, the magnetically hard powders based on Pr(Fe,V)₁₂N_1.6 are obtained with a maximum energy product of 135 kJ/m³ (16.9 MGOe) and a remanence of 1.18 T at room temperature.