Crystal structure,electrical, and magnetic properties of the Sm2Cu0.8Ge3 compound

The crystal structure, electrical, and magnetic properties of the new ternary compound Sm₂Cu_0.8Ge₃ have been investigated using powder X-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. X-ray diffraction patterns reveal that this compound crystallizes in a tetragonal α-ThSi₂ structure (space group I4₁/amd) with lattice parameters a = 0.413(1) nm and c = 1.420(3) nm. The irreversibility of the zero field cooled and field cooled dc magnetization data reveals the occurrence of spin glass transition with the spin freezing temperature T_f ∼ 8.5 K in this compound. Ac susceptibility and isothermal remanent magnetization data also confirm the existence of the spin glass phase. In addition, a broad maximum is observed in the ρ(T) curve near T_f. The spin glass phase is ascribed to the formation of random interaction between the Sm ions due to the irregular distribution of Cu and Ge atoms as well as the deficiency of the occupancy on the 8e crystallographic sites of the sample.     

Low-dimensional magnetic behaviour of new radical-ion salts: (BEDT-TTF)2[AuIII(i-mnt)2] and (BEDT-TTF)2[BiBr4]

Electrical and magnetic properties of two new radicalion salts of BEDT-TTF (BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene) are reported. (BEDT-TTF)₂[Au^III(i-mnt)₂] (i-mnt is 1,1-dithio-2,2-dicyano-ethylene) is a semiconductor, σ_r.t. = 2.0 × 10⁻¹−5.5 × 10⁻² S cm⁻¹ with a temperature dependent activation energy (0.14–19 eV). The powder magnetic susceptibility (10–300 K) has been fitted according to a uniform antiferromagnetic (S = 1/2) Heisenberg model by using the experimental g value of 2.0067 and a magnetic exchange constant J/k_B of −110 K. (BEDT-TTF)₂ [BiBr₄] shows similar electrical and magnetic behaviour with σ_r.t. = 5 × 10⁻² S cm⁻¹ on a powdered sample and J/k_B = − 79 K. At low temperature impurities are responsible for the Curie-like behaviour.     

2D double-layered metal–radical complexes: Crystal structures and magnetic properties

Two new complexes [Mn(NIT4Py)(2,4-PDA)(H₂O)₂] (1) and [Co(NIT4Py)(2,4-PDA)(H₂O)₂] (2) (where NIT4Py stands for 2-(4′-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, 2,4-PDA stands for pyridine-2,4-dicarboxylate) have been synthesized and characterized. The single-crystal X-ray diffraction demonstrates that complex 1 present dimeric structure with two 2,4-PDA anions function as bridging ligands, connecting two Mn(II) centers. The dimeric units form an infinite 2D double-layered network via hydrogen bonds. Complex 2 consists of infinite 1D chain, in which each 2,4-PDA anion bridges two adjacent Co(II) ions in monodentate–bidentate mode. These 1D chains are further connected together by hydrogen bonds, generating a 2D double-layered structure, too. The variable temperature magnetic susceptibility measurements reveal that the magnetic couplings between Mn(II) and NIT4Py, Co(II) and NIT4Py are weak ferromagnetic and antiferromagnetic interactions for complexes 1 and 2, respectively.     

Structure and magnetic properties of strontium ferrite anisotropic powder with nanocrystalline structure

The phase composition, nanocrystallite size, lattice microstrain and particles morphology of a SrFe₁₂O₁₉ powder subjected to milling and subsequent annealing were studied by various methods. The investigations showed that the high-temperature annealing of the preliminarily milled powder resulted in the increase in the coercive force (μ₀Н_сi) of the SrFe₁₂O₁₉ powder up to 0.4 T owing to the formation of nanocrystalline structure (D ∼ 10³ nm) with low lattice microstrains. However, the annealed powder cannot be textured in an applied magnetic field because of random orientations of the crystallites in powder particles. A processing technique, which includes the low-temperature annealing of powder in an applied magnetic field, was suggested. It allowed us to produce the anisotropic powder of the strontium ferrite with the nanocrystalline structure that ensures the high coercive force of the powder (∼0.4 T) and possibility of the powder texturing in the magnetic field. The prepared samples textured in a magnetic field exhibit the higher both remanence (by a factor of 1.4) and energy product (by a factor of 2.1) as compared to those of isotropic SrFe₁₂O₁₉ samples.     

Hydrogen absorption and Fe Mössbauer effect in UFeGe

Hydrogenation of UFeGe transforms the monoclinic type of structure into the orthorhombic (TiNiSi-type) and subsequently to the hexagonal (ZrBeSi-type) structure. It does not induce magnetic order, however magnetic susceptibility is enhanced. The Sommerfeld coefficient γ increases from 12 mJ/mol K² in UFeGe to 36 mJ/mol K² in UFeGeH_1.7-1.8 (β-hydride). The observed variations of electronic properties are mainly due to the modified geometry of the lattice, characterized by enhanced inter-uranium spacing, and reduced 5f-3d hybridization in the hydrides.     

Crystal structure and magnetic properties of the new ternary actinide compounds AnPd5Al2 (An = U, Np)

We report the crystal structure and magnetic properties of new ternary actinide compounds UPd₅Al₂ and NpPd₅Al₂. Both compounds crystallize in the body-centered tetragonal ZrNi₂Al₅-type tetragonal structure (I 4/mmm). Although the magnetic susceptibility of both compounds follows the Curie–Weiss behavior at high temperature, no magnetic phase transition was observed. UPd₅Al₂ has a nonmagnetic ground state where the magnetic susceptibility saturates at low temperature, while NpPd₅Al₂ superconducts below 4.9 K as reported recently.     

Magnetic structure of Tb2CuIn3

The intermetallic compound Tb₂CuIn₃ has been studied by means of neutron diffraction at various temperatures ranging from 293 to 3.8 K. Data analysis of the high temperature region confirms the hexagonal crystal structure (space group P6/mmm) with Tb at 1a, Cu and In statistically distributed at 2d positions. The unit cell constants are a=4.702(1) Å and c=3.682(2) Å. Below 33 K, Tb₂CuIn₃ undergoes a magnetic phase transition into a collinear antiferromagnetic structure described in an orthorhombic unit cell with A=a, B=a√3, C=c. Terbium magnetic moments of 6.8 μ_B at 3.8 K are oriented along the c axis. Complementary susceptibility measurements confirm the transition temperature. The magnetic isotherm at 5 K in fields with μ_oH up to 7 T is far from saturation.     

Magnetic properties, crystal and electronic structure of GdNi5−xCux series

The effect of Ni/Cu substitution on the magnetic properties, crystal and electronic structure of the polycrystalline GdNi_5−xCu_x series has been studied. All compounds crystallize in the hexagonal CaCu5 type of crystal structure (space group P6/mmm). The temperature dependence of magnetic phase transition (T_mag) estimated from χ_AC(T) susceptibility as well as magnetization M(T) below room temperature indicates the maximum for x = 1.0 copper concentration. In the paramagnetic range (above 300 K) the magnetic susceptibilities follow a Curie-Weiss-type dependence. The effective magnetic moments are higher than theoretical value for free Gd³⁺.From X-ray photoelectron spectroscopy (XPS) data the valence band as well as the core level spectra have been analyzed. The filling of Ni3d band in the GdNi_5−xCu_x system by charge transfer of Gd conduction electrons is revealed by a reduction of the satellite intensities in the Ni2p core level spectrum. The obtained results exhibit that the valence bands at the Fermi level are dominated by hybridized Ni3d and Gd5d states, when Cu3d states are rather localized about 3 eV below the Fermi level. Quite good relation between the magnetic properties and electronic structure has been found.     

Negative magnetization, magnetic anisotropy and magnetic ordering studies on Al-substituted copper ferrite

Detailed magnetic properties of Al³⁺-modified CuFe₂O₄ spinel ferrite system: CuAl_xFe_2−xO₄; x = 0.0, 0.2, 0.4 and 0.6, have been studied by means of X-ray powder diffraction, field cooled (FC) and zero field cooled magnetization (ZFC) (H = 10 mTesla, T = 4-325 K), magnetic hysteresis (H_max = 2 Tesla, T = 10 and 300 K) and low field (40 A/m) ac susceptibility (T = 300-750 K) measurements. The system exhibits canted spin structure. It has been shown that the observed features of the FC-ZFC magnetization and ac susceptibility curves arise due to the low magneto crystalline anisotropy, not due to the cluster spin-glass-like magnetic ordering. The interesting features like low temperature cusp in the ZFC magnetization for all the compositions and negative magnetization for x = 0.6 composition have been observed. An attempt has been made to explain the negative magnetization within the framework of available models.     

Magnetic properties of the new rare earth intermetallic compound Pr5AgSn3

A detailed structural characterisation, by means of the powder X-ray diffraction method, of the new Pr₅AgSn₃ intermetallic compound has been performed and a.c., d.c. magnetic measurements in the 4-300 K temperature range and in applied magnetic fields up to 9 Tesla have been obtained and analysed. The compound orders ferromagnetically below 33.5 K and exhibits a pronounced hysteresis cycle at 5 K with a saturation magnetisation (μ_sat) of 1.84 μ_B/Pr atom. In the paramagnetic state the compound follows the Curie-Weiss law with μ_eff.=3.40 μ_B and θ_P=+32 K. The splitting of the peak in the a.c. susceptibility by applied low d.c. fields as well as the temperature dependence of the remanence (B_r) and of the coercive field (H_c) are tentatively explained in terms of domain dynamics.     

Crystal structure and physical properties of a new intermetallic compound URu2Al10

We report on the existence in the U–Ru–Al system of a novel compound, URu₂Al₁₀, crystallizing in the orthorhombic YbFe₂Al₁₀-type structure, where the uranium atoms are caged in Ru–Al polyhedra, forming a clathrate-like structure. Results of the magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to 8 T, thermopower and specific heat, performed in a wide temperature range, are presented. No magnetically ordered state down to the lowest temperature measured has been found. On the basis of (i) the susceptibility anomaly occurring at about 50 K and (ii) the positive magnetoresistivity, growing with applied magnetic field as αBⁿ (n ≈ 3/2), (iii) a characteristic temperature variation of the thermopower, as well as (iv) a moderate value of the Sommerfeld coefficient, a mixed-valence state of uranium in this compound has been postulated. This points to similarities between the presently studied compound and the behaviour of other Ru-containing uranium ternaries, such as U₂Ru₂Sn and U₂RuGa₈, classified earlier as valence-fluctuating type materials.     

X-ray photoelectron spectroscopy and magnetic properties of CeCo7Mn5 and CeCo8Mn4 isostructural ThMn12 type compounds

The magnetic properties of CeCo₇Mn₅ and CeCo₈Mn₄ compounds have been investigated by combining X-ray photoelectron spectroscopy (XPS) and magnetic measurements in a wide temperature range (4–550) K and magnetic field up to 12 T. X-ray powder diffraction (XRD) measurements showed that CeCo₇Mn₅ and CeCo₈Mn₄ compounds are isostructural and crystallize in the ThMn₁₂ structure type. XPS spectra pointed out the intermediate valence state of Ce atoms and that both Co and Mn atoms carry magnetic moments. The complex magnetic structure of CeCo₇Mn₅ and CeCo₈Mn₄ is determined by the competition between the ferromagnetic (Co–Co pairs) and antiferromagnetic (Co–Mn and Mn–Mn pairs) interactions. Two different ordering temperatures T_N and T_C correlated to antiferromagnetic and ferromagnetic coupling of 3d magnetic moments, respectively, are evidenced. Magnetic moments of about 1.6 μ_B/Co and 3.2 μ_B/Mn atoms were determined by correlating the magnetic data of the two compounds, in good agreement with the exchange splitting of XPS Co 3s and Mn 3s core levels.     

Antiferromagnetic ordering below 1.7 K in PrIr2Ge2

We present our investigations on magnetic and transport properties of polycrystalline PrIr₂Ge₂ which forms in CaBe₂Ge₂-type primitive tetragonal structure (space group P4/nmm). The ac magnetic susceptibility data exhibit two well pronounced peaks at 2.08 K and 0.76 K due to the onset of magnetic order. The specific heat also exhibits a sharp λ-type anomaly at 1.7 K confirming the onset of bulk antiferromagnetic order. The temperature dependence of magnetic part of entropy suggests a quasi-triplet ground state in this compound. The onset of magnetic order is also confirmed by the electrical resistivity data.     

The formation of 1T and 2H titanium disulfide by deintercalation of NaxTiS2

The topochemical reaction of Na_xTiS₂ solid phases with I₂ in acetonitrile leads to several modifications of TiS₂. The 1T-TiS₂ modification, Cd(OH)₂ type, is found by deintercalation of the rhombohedral phases 3R(I)-Na_xTiS₂ and 3R(II)-Na_xTiS₂. Deintercalation of the hexagonal phase 2H(I)-Na_xTiS₂ leads to a strongly disordered 2H-TiS₂ phase with a chch stacking of sulfur. The structure is in agreement with a mechanism of deintercalation consisting of parallel displacements of TiS₂ sandwiches.The observed magnetic susceptibility of powder 2H-TiS₂ is discussed in terms of a nearly temperature-independent intrinsic contribution of about 14 × 10^?6 emu per mole and a Curie-like tail contribution due to about 3 × 10^?4 mole of localized paramagnetic Ti²⁺ (3d²).     

Magnetic structure of Er6Ni2Sn

The crystallographic and magnetic structures of Er₆Ni₂Sn have been determined at low temperatures using neutron powder diffraction. It has been found that this system orders antiferromagnetically (AF) below T_N = 17 K. Data taken at low temperatures and analyzed using symmetry group analysis suggest that Er₆Ni₂Sn forms a complex non-collinear commensurate AF structure with strongly reduced Er magnetic moments. The reason for the reduced moments is unclear and needs further studies. The magnetic phases below 7 K and in the temperature range 7–17 K differ only in the Er magnetic moment magnitudes and in the angle that the Er moments at the 8l site make with the c-axis. The extra reflections present in the powder diffraction patterns suggest presence of a secondary phase. The temperature evolution of the powder pattern indicates that the secondary phase orders AF at 35 K.     

Crystal structure and magnetic properties of pseudobinary solid solutions Pr(In1 − x Pb x )3

Structure and magnetic properties of Pr(In_{1 ? x} Pb _x )₃ alloys have been studied in some detail. It has been shown that, in this system, in the whole range of compositions (0 ≤ x ≤ 1), there is a continuous series of disordered solid solutions with a structure of the Cu₃Au type. The lattice parameter of these solid solutions varies linearly (according to Vegard’s law). The temperature dependence of the magnetic susceptibility has been studied in the temperature range of 2–300 K. At enhanced temperatures, it is described well by the Curie-Weiss law for all alloys. At low temperatures, an anomalous deviation from this law for the terminal alloys is observed, which is especially strong for PrIn₃. In pseudobinary alloys, this anomaly weakens and the magnetic susceptibility itself increases. In the concentration dependence of the susceptibility measured at 2 K, a maximum is observed. The specific features of the dependence of the magnetic susceptibility of pseudobinary alloys on the temperature and concentration x have been explained by a decrease in the local symmetry of crystal field at the sites of Pr³⁺ ions due to the partial random replacement of their nearest neighbors by atoms of different valences.     

Nd2Ni2MgH8 hydride: Synthesis,structure and magnetic properties

Hydrogen interaction with intermetallic compound Nd₂Ni₂Mg crystallizing in the tetragonal Mo₂FeB₂ type of structure leads to the formation of hydride/deuteride containing 7.4–8 H(D)/f.u. Hydrogen absorption is accompanied by a monoclinic deformation of the unit cell with the crystal structure data refined from Synchrotron XRD (Sp. gr. P2₁/c; a = 11.60733(5) Å; b = 7.66057(3) Å; c = 11.78743(5) Å, β = 92.4126(4)°, V = 1047.194(8) ų) and high resolution powder XRD data. The formed interstitial hydride disproportionates during heating forming NdH₂. Nd₂Ni₂Mg is an antiferromagnet with the Néel temperature T_N ≈ 19 K. Presence of another magnetic phase transition at 14 K together with two metamagnetic transitions indicates a complicated magnetic phase diagram. The hydrogenation reduces T_N to 1.0 K.     

Magnetic and crystal structure of Th–Fe–Sn intermetallics: ThFe0.22Sn2 and Th4Fe13Sn5

The crystal and magnetic structures of two new ternary phases in the Th–Fe–Sn system: ThFe_0.22Sn₂ and Th₄Fe₁₃Sn₅ have been investigated by high-resolution neutron powder diffraction. The ThFe_0.22Sn₂ phase crystallizes in an orthorhombic crystal structure, space group Cmcm, whilst Th₄Fe₁₃Sn₅ crystallizes in the tetragonal space group P4/mbm. In agreement with bulk magnetization measurements, the compound ThFe_0.22Sn₂ does not order magnetically in the temperature range investigated, while Th₄Fe₁₃Sn₅ orders below 375 K, with the easy magnetization direction of the Fe moments aligned along the tetragonal c-axis.     

Quantum chemical study of some cyclic nitrogen compounds as corrosion inhibitors of steel in NaCl media

Corrosion inhibition efficiencies of 3-amino-1,2,4-triazole (3-ATA), 2-amino-1,3,4-thiadiazole (2-ATDA), 5-(p-tolyl)-1,3,4-triazole (TTA), 3-amino-5-methylmercapto-1,2,4-triazole (3-AMTA) and 2-aminobenzimidazole (2-ABA) as corrosion inhibitors on steel in sodium chloride media were investigated by using semiempirical PM3 and density functional theory (DFT) methods. Quantum chemical parameters such as highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), energy gap (ΔE) and dipole moment (μ) have been calculated for these compounds by using semiempirical PM3 and 6-31G(d), 6-311G(d,p) DFT methods. It was found that theoretical data support the experimental results.     

Structural and physical properties of the U9Fe7Ge24 uranium germanide

A new ternary compound, U₉Fe₇Ge₂₄, was synthesized by arc-melting the elements, followed by annealing at 900 °C. This compound was characterized by single crystal and powder X-ray diffraction, magnetization, specific heat and electrical transport measurements. It crystallizes in an original tetragonal structure type (space group I4/mmm), with lattice parameters a = 12.3789(2) Å and c = 18.2881(3) Å. Three uranium, eighth germanium, and three iron crystallographic sites exist in this structure, with the atoms making a stacking of infinite chains along the a and b axis. From their interatomic distances strong interactions between the uranium and germanium atoms can be predicted. The magnetic and specific heat measurements down to 2 K do not show any magnetic transition. The Curie–Weiss behaviour with a negative paramagnetic Curie temperature θp = ?94 K and reduced effective magnetic moment of μ_eff = 2.13 μ_B/U indicate that the compound is rather far from onset of magnetism, presumably due to a strong hybridisation of the 5f and ligand states. The electrical transport measurements show a metallic behaviour.