Nuclear spin-lattice and nuclear spin-spin relaxation time measurements in EuB6 at low temperatures using the spin-echo technique

Experimental results on the nuclear spin-lattice and nuclear spin-spin relaxation times in the ferromagnetic EuB₆ at temperatures below 4·2 K are presented using the external magnetic field,H _ext, in the range of 0 ⩽H _ext ⩽ 10 kG. Nuclear spin-spin relaxation time computed on the basis of the Suhl-Nakamura process turns out to be 3·2μs, which compares well with the experimental value 11·1μs obtained with the 10 kG magnetic field at 1·7 K. It is found that in the ferromagnetic EuB₆,T ₁ is approximately 5 × 10³ times larger thanT ₂ at 1·7 K with the 10 kG magnetic field. Thus the effect ofT ₁ onT ₂ can be neglected. From the experimental value ofT ₂, the value of the homogeneous line broadening is found to be 14 kHz. The corresponding value obtained from the cw method is 175 kHz. This evidently shows the presence of the inhomogeneous line broadening in the cw NMR.     

Thermal behavior of gamma-irradiated urea–formaldehyde composites based on the differently activated montmorillonite K10

Journal of Thermal Analysis and Calorimetry - This work investigated the thermal characteristics of irradiated composite materials formulated on the urea–formaldehyde resin (UF) and...     

Specific capacitance of CoS encapsulated g-C3N4 core shell nanocomposite as extremely efficient counter electrode in quantum dots solar cells

Journal of Solid State Electrochemistry - In this context, the electrical conductivity and surface activity of cobalt sulphide (CoS) as counter electrode CE is improved by incorporating with...     

Spectroscopic Characterizations of Metal-Complexes of 4-Hydroxybenzoic Acid With the Ni(Ⅱ), Mn(Ⅱ), and Cu(Ⅱ) Ions

One of the phenolic acids is 4-hydroxybenzoic acid (HBA) which takes the form of a white crystalline solid with a molecular formula of C₇H₆O₃, a melting point of 214.5 ℃ and a molecular weight of 138.12 g·mol-1. It soluble in polar organic solvents like acetone and alcohols, and slightly soluble in chloroform and water. The reactions between the metal ions and the HBA were carried out under specific conditions like (molar reaction was 2∶2 (ligand to metal), reaction temperature was 60 ℃, media was neutral (pH 7), and solvent was H₂O ∶MeOH (1∶1). Under these conditions, the HBA was deprotonated to form (HOC₆H₄CO-₂; L-). The ligand L- was coordinated to the metal ions forming the metal complexation. The reaction of 4-hydroxybenzoic acid (HOC₆H₄CO₂H; HL) with the Ni(Ⅱ), Mn(Ⅱ) and Cu(Ⅱ) ions afford metal-complexes with gross formula of [Ni₂L₂(NO₃)₂(H₂O)₄], [Mn₂L₂(NO₃)₂(H₂O)₄] and [Cu₂L₂(NO₃)₂(H₂O)₄], respectively. These complexes were characterized by elemental analysis (CHN), magnetic susceptibility, UV-Vis spectra, infrared (IR), and X-ray powder diffraction (XRD) techniques. The complexes of HBA are insoluble in common solvents and hence molar conductance could not be measured, but this very insolubility indicates that the complexes are neutral. Data has demonstrated that the ligand (L-) was coordinated to the metal ion by bidentate bridging carboxylate group (COO-), with an octahedral geometry. Thus, HBA is expected to act as bidentate uninegative ions and the coordination number of the metal ions is six. XRD results showed that the complexes possess uniform and organized microstructures in the nanometer range with a main diameter in the range of 11～28 nm.     

Synthesis and characterization of a reduced heteropoly-tungstovanadate: (NH4)7[VvO4W 10IV V 2IV O36].ca. 22H2O

The compound (NH₄)₇[ V^vO₄W ₁₀ ^VI V ₂ ^VI O₃₆]·ca.22H₂O (1) has been synthesized from an aqueous ammonium acetate buffer (pH 4) containing sodium vanadate, sodium rungstate_and sodium dithionite. Compound (1) crystallizes in a cubic space groupFm — 3, witha = 22.2001(6) ? and Z = 8. The anion [V^vO₄W ₁₀ ^VI V ₂ ^IV O₃₆]^7- is a typical Keggin type structure with V^VO₄ as the central tetrahedron. (1) has further been characterized by elemental analyses, redox titration, IR, EPR, and electronic spectroscopy and room temperature magnetic moment measurement.     

The impact of decision timing on the suppliers’ interactions: simultaneous moves <Emphasis Type="Italic">versus</Emphasis> sequential moves

The last few decades have witnessed a huge growth of outsourcing in industry where the downstream firm assigns its production tasks to different upstream suppliers. This makes the supply chain structure more complicated and gives rise to some relevant operational questions. This paper focuses on a supply chain structure that consists of one assembler and two suppliers, and both suppliers’ production yields are stochastic. The assembler delegates the quantity decisions to the suppliers, and the two suppliers choose their production quantities either simultaneously or sequentially. We compare the suppliers’ equilibrium production strategies under these two scenarios. Our results show that the decision sequence can exert significant influences on the firm’s and channel’s equilibrium payoffs. At any given wholesale price, both suppliers produce more components under sequential moves than under simultaneous moves, and this results in higher payoffs for the suppliers, the assembler and the entire supply chain. The supplier’s profit increases if he can make the decision later under sequential moves. From the channel’s perspective, it is more beneficial for the supplier with a higher production cost to make the decision first. The assembler is able to extract more surplus by endogenously setting the wholesale price. However, this may make the suppliers worse off under sequential moves than under simultaneous moves.     

An adaptive finite element method in reconstruction of coefficients in Maxwell’s equations from limited observations

We propose an adaptive finite element method for the solution of a coefficient inverse problem of simultaneous reconstruction of the dielectric permittivity and magnetic permeability functions in the Maxwell’s system using limited boundary observations of the electric field in 3D.     

Bringing an important macrocycle into a polyoxometalate matrix: synthesis, crystal structure, spectroscopy and electrochemistry of [Co(III)(transdiene)(Cl)2]2[Mo6O19], [Ni(II)(transdiene)][W6O19]·DMSO·DCM and [Zn(II)(transdsiene)(Cl)]2[W6O19

Three polyoxometalate based ion pair solids (1-3), in which Co(III) (d(6)), Ni(II) (d(8)) and Zn(II) (d(10)) complexes of a tetra-aza macrocycle, Me(6)-trans-[14]-diene act as the cationic moieties, have been reported. The title complexes, formulated as [Co (C(16)H(32)N(4))(Cl)(2)](2)[Mo(6)O(19)] (1), [Ni(C(16)H(32)N(4))][W(6)O(19)]·DMSO·DCM (2) and [Zn(C(16)H(32)N(4))(Cl)](2)[W(6)O(19)] (3) (C(16)H(32)N(4) = Me(6)-trans-[14]-diene), are the first crystallographic paradigms where transition metal complexes of a Schiff condensed tetra-aza macrocycle have been associated with an isopolyanion, [M(6)O(19)](2-) (M = Mo(vi) and W(vi)). Compounds 1-3 have been characterized through routine spectroscopic analyses including elemental analysis and their structures have been unambiguously determined through single crystal X-ray crystallography. The molecules of compound 1 assemble obeying P1 (#2) space symmetry, whereas those of compounds 2 and 3 follow the higher symmetrical ensemble P2(1)/c (#14). The ESR spectral studies of compounds 1-3 have revealed their diamagnetic (low-spin) nature. The last part of this article describes the electrochemical properties of the title compounds.     

Protonation of an Oxo‐Bridged Diiron Unit Gives Two Different Iron Centers: Synthesis and Structure of a New Class of Diiron(III)‐μ‐hydroxo Bisporphyrins and the Control of Spin States by Using Counterions

Reported herein is a hitherto unknown family of diiron(III)‐μ‐hydroxo bisporphyrins in which two different spin states of Fe are stabilized in a single molecular framework, although both cores have identical molecular structures. Protonation of the oxo‐bridged dimer ( 2 ) by using strong Brønsted acids, such as HI, HBF₄, and HClO₄, produce red μ‐hydroxo complexes with I₃^? ( 3 ), BF₄^? ( 4 ), and ClO₄^? ( 5 ) counterions, respectively. The X‐ray structure of the molecule reveals that the Fe? O bond length increases on going from the μ‐oxo to the hydroxo complex, whereas the Fe‐O(H)‐Fe unit becomes more bent, which results in the smallest known Fe‐O(H)‐Fe angles of 142.5(2) and 141.2(1)° for 3 and 5 , respectively. In contrast, the Fe‐O(H)‐Fe angle remains unaltered in 4 from the corresponding μ‐oxo complex. The close approach of two rings in a molecule results in unequal core deformations in 3 and 4 , whereas the cores are deformed almost equally but to a lesser extent in 5 . Although 3 was found to have nearly high‐spin and admixed intermediate Fe spin states in cores I and II, respectively, two admixed intermediate spin states were observed in 4 . Even though the cores have identical chemical structures, crucial bond parameters, such as the Fe? N_p, Fe? O, and Fe???Ct_p bond lengths and the ring deformations, are all different between the two Fe^III centers in 3 and 4 , which leads to an eventual stabilization of two different spin states of Fe in each molecule. In contrast, the two Fe centers in 5 are equivalent and assigned to high and intermediate spin states in the solid and solution states, respectively. The spin states are thus found to be dependent on the counterions and can also be reversibly interconverted. Upon protonation, the strong antiferromagnetic coupling in the μ‐oxo dimer (J, ?126.6 cm^?1) is attenuated to almost zero in the μ‐hydroxo complex with the I₃^? counterion, whereas the values of J are ?36 and ?42 cm^?1, respectively, for complexes with BF₄^? and ClO₄^? counterions.