Simultaneous determination of aluminum (III) and iron (III) by first-derivative spectrophotometry in alloys

A highly sensitive and selective first-derivative spectrophotometric method has been developed for the determination of aluminum and iron in mixtures. The method is based on the formation of the binary complexes of aluminum and iron with Alizarin yellow R (AYR) 5-[4-nitrophenylazo]salicylic acid at pH 2.0 with molar absorptivity of 1.1∙10⁴ l⋅mol^–1⋅cm^–1. A zero-crossing technique is found suitable for the direct measurement of the first derivative value at the specified wavelength, so aluminum and iron were thus determined in the ranges 1.3–5.4 μg/ml and 1.1–8.3 μg/ml, respectively, in the presence of both components. The detection limits were found to be 1.4 ng/ml for aluminum and 2.8 ng/ml for iron. The relative standard deviations were in all cases less than 1.5%. The proposed method was successfully applied for the simultaneous determination of aluminum and iron in certified reference aluminum samples.     

A study of trinuclear iron(III) O-phthalates

Mössbauer data as well as infrared and magnetic susceptibility results indicate that Fe(III)-phthalates are high spin ferric complexes with a combination of trinuclear oxo-bridged and monomer structures. Values obtained for the isomer shift and quadrupole splitting parameters suggest that different counter ions, such as OH, NO₃, and Na, leave the Fe(III) ions in two very distorted octahedral arrangements, although they scarcely affect the electron densities at the iron nuclei.     

Reduction of iron(III) in annealed asbestos/chrysotile

Magnetic and structural properties of Bi substituted YIG with nominal formula of Bi _x Y_3???x Fe₅O₁₂ (x?=?0.0, 0.25, 0.5, 0.75, 1.00) prepared via Mechanochemical Processing (MCP) have been studied with Mossbauer spectroscopy, X-ray diffraction (XRD). The temperature dependence of sublattice magnetic hyperfine field for samples is analyzed. The a–d intersublattice superexchange found to be antiferromagnetic and increases from ??21.97 to ??25.79 k_B as Bi increases from 0.0 to 0.25. The a–a and d–d intrasublattice exchanges for sample x?=?0.0 are 13.18 and 10.55 k_B respectively while for sample x?=?0.25 a–a and d–d intrasublattice exchanges are 7.7 and 8.9 k_B respectively. The correlation of lattice constant and superexchange interaction are discussed.     

Heat capacity of a five-coordinated iron(III) complex,iodobis (N,N-Dimethyldithiocarbamato) iron(III), between 0.4 and 300 K

The heat capacity of iodobis (N, N-dimethyldithiocarbamato)iron(III) has been measured between 0.4 and 300 K. Based on the heat capacity and entropy at low temperatures it was found that the present sample consists of a mixture of monomer (ca. 40%) and dinier (ca. 60%); the former brings about a λ-type phase transition from an antiferromagnetic to a paramagnetic state at T_N = (1.65 ±0.04) K while the latter exhibits a Schottky-ype anomaly due to antiferromagnetic dimeric coupling, the effect of which becomes dominant below ca. 0.7 K. The zero-field splitting parameter of a single ferric ion was estimated to be $\text{D}\text{k}\text{=}\text{D}{}_{\mathrm{D}}\text{k}\text{= 14 K}$ for the monometer and the dimer, while the dimeric coupling constant was $\text{J}{}_{\mathrm{D}}\text{k}\text{= ?0.15 K}$. The entropy at low temperatures cannot be accounted for solely by the spin manifold. Additional contribution from a tunnel-splitting of the rotational levels of four constituent methyl-groups has been discussed. In this case, the level splitting of the ground state is 2.5 J mol^?1 and the barrier height of hindering potential is 2.3 kJ mol^?1.     

Conductivity anisotropy in the antiferromagnetic state of iron pnictides

Recent experiments on iron pnictides have uncovered a large in-plane resistivity anisotropy with a surprising result: The system conducts better in the antiferromagnetic x direction than in the ferromagnetic y direction. We address this problem by calculating the ratio of the Drude weight along the x and y directions, D(x)/D(y), for the mean-field Q=(π,0) magnetic phase diagram of a five-band model for the undoped pnictides. We find that D(x)/D(y) ranges between 0.2相似文献   

Spin-spin relaxation in heteropolynuclear clusters containing iron(III) and copper(II) ions

The magnetic coupling between Fe(III) and Cu(II) and the relaxation behavior of the spin centered at the iron have been studied in di- and trinuclear clusters. The experimental spectra have been analyzed in terms of a simple cross-relaxation model. In the strongly coupled trimer the relaxation rates are determined by a Boltzmann factor and a single field- and temperature-independent scaling parameter¹ w ₀, while the weakly coupled dimer exhibits obviously a more complex behavior.     

Magnetic properties of calcium-silicates (diopside and gehlenite) doped with iron (III)

The incorporation of Fe³⁺ cations into some Ca-silicates (diopside, gehlenite), substituting for alkali earths of different valencies and in differently coordinated lattice positions, will give rise to considerable lattice disorder. It is shown that this will result in special magnetization properties of these silicates.     

Intermolecular potential and equilibrium orientational states for dimers of non-polar molecules

The anisotropic intermolecular potential V(r ?₁ ?₂ ?) of two non-polar molecules, with its arbitrary coefficients represented by the functions of the intermolecular distance r, is formulated and analytically minimized in the angular variables ?₁, ?₂ and ? = ?₁ ??₂. In terms of multipole expansion, the explicit form of these coefficients is strictly specified by the constants of quadrupole, dispersion, and repulsive interactions of two non-polar molecules. These coefficients are also obtainable from basic orientational configurations computed by ab initio methods. As a result, the intermolecular potential V(r) can be found and equilibrium orientational states can be characterized at each value of r. An analysis of literature data for the H₂, N₂, and O₂ dimers together with ab initio calculations of V(r, ?₁, ?₂ ?) for the H₂ and N₂ dimers (performed by the MP2 and CCSD(T) methods with the cc-aug-pvqz basis set) demonstrate that the analytical form proposed for the angular dependence of V and the result of its minimization are helpful in revealing intermediate orientational phases in which angular variables change continuously with r, and the function V(r) has regions with a mild slope. One such phase with ?₁ = ?₂, ? = 0 has been found to correspond to the global minimum of the N₂ dimer.     

A finite size analysis of the structure factor in the antiferromagnetic Heisenberg (AFH) model

From a finite size analysis we extract the structure factorS(p, N=) of the one dimensional AFH-model in the groundstate: The gross structure is well described byL (p) = –ln(1– ^p ). The fine structure which only contributes a few percent reveals a pronounced non-linear behavior inL(p) with a maximum atp=0.20 and a minimum atp=0.82.     

Characterization of iron(III) oxide films used for photoelectrode by means of cems

Thin iron oxides deposited on semi-conductive glass by a spray pyrolysis technique were analysed by Conversion Electron Mössbauer Spectrometry (CEMS). Iron oxide deposited on SnO₂ coated glass was composed of a large grained particles of crystalline α?Fe₂O₃, which showed sextet. The doublet and sextet appeared in CEM spectra of iron oxides deposited on In₂O₃ and WO₃ coated glasses. The sextet was due to α?Fe₂O₃ and the doublet was attributted to the superparamagnetic microcrystalline α?Fe₂O₃ (≈15nm) rather than to spinel compounds of iron. The iron oxide deposited on ZnO coated glass gave a doublet in CEM spectra. It was supporsed to be due to very fine particle of α?Fe₂O₃ (<100nm). It was found that iron oxide films obtained by spray pyrolysis were dependent on the kinds and the temperature of the semi-conductive materials coated on glass.     

Sonochemical synthesis of amorphous nanoscopic iron(III) oxide from Fe(acac)3

Amorphous nanoscopic iron(III) oxide with interesting magnetic properties was prepared by sonolysis of Fe(acac)(3) under Ar in tetraglyme with a small amount of added water. The organics content and the surface area of the Fe(2)O(3) nanoparticles can be controlled with an amount of water in the reaction mixture and it increases from 48 m(2)g(-1) for dry solvent up to 260 m(2)g(-1) when wet Ar is employed. For further monitoring of the particle size and morphology and for the study of the surface, magnetic and thermal properties, the sample with 2 vol.% of H(2)O was chosen. SEM showed nanoscopic composite particles of a uniform size distribution and nearly spherical shapes with an estimated diameter of 20 nm. Such composites are built from amorphous iron(III) oxide nanoparticles (3 nm) embedded in an acetate matrix as proved by TEM and IR spectroscopy. Temperature-dependent M?ssbauer spectra demonstrate a very narrow magnetic transition with an unusually low transition temperature around 25K reflecting the system of magnetically non-interacting ultrasmall particles with a narrow size distribution. The in-field (5T) M?ssbauer spectrum recorded at 5K shows a minimum change compared to the zero-field spectrum indicating an absence of the long-range magnetic ordering. The composite particles are thermally stable up to 150 degrees C, which is confirmed by DSC, TG, and by the constant surface area. At higher temperatures, acetate groups are removed from the particle surface, which is documented by the increased surface area and disappearance of their IR bands.     

Ferromagnetic and antiferromagnetic properties of the blume-capel model in (1+1) and (2+1) dimensions

A renormalization group realization, allowing the simultaneous and analytic study of both the ferromagnetic and antiferromagnetic phases of the Blume-Capel model, is applied in (1+1)_and (2+1) dimensions. The model is also analyzed by using a variational technique. Critical and tricritical parameters are determined and the phase diagram is exhibited.Partially supported by CONICET, CIC Pcia. de Buenos Aires and SUBCYT, Argentina     

Heat capacity of a five-coordinated iron(III) complex with spin S = 32, bromobis(N,N-diethyldithiocarbamato)iron(III), between 0.4 and 300 K

Heat capacity measurements have been made for six kinds of specimens prepared by different methods. Among them, Sample A exhibited a A-type ferromagnetic pahse transition at 1.347 K and a Schottky-type anomaly due to the zero-field splitting around 9K. The total entropy and enthalpy were (11.05 ± 0.04) J K^?1mol^?1 and (97.0 ± 0.4) J mol^?1, respectively. Sample B exhibited a Sehottky-type anomaly around 0.4 K due to the ferro-magnetic dimeric coupling with $\text{J}{}_{\mathrm{D}}\text{k}\text{= + 0.30}\text{K}$ as well as the Schottky-type anomaly at 9K. The total magnetic entropy and enthalpy were (11.45 ± 0.03) JK^?1 mol^?1 and (93.8 ± 0.8) J mol^?1, respectively. The remaining samples are simple mixtures of the λ-type modification and the dimeric modification. Irrespective of the magnetic behavior at low temperatures, all the samples showed a non-magnetic first-order phase transition around 270 K. The heat capacity and entropy of this phase transition have been accounted for in terms of the Frenkel theory of heterophase fluctuation. Construction of an adiabatic-type calorimeter workable between 1.5 and 393 K has been also presented.     

Parameter dependence of optical conductivity in antiferromagnetic phase of iron pnictides

We investigate the optical conductivity of iron pnictides in antiferromagnetic state by mean-field calculation in a five-band Hubbard model, focusing on its anisotropic behavior by examining several states calculated with different Hund coupling J, such as the states with a low or high magnetization and with or without a strong orbital ordering. In addition, we investigate the J dependence of the Dirac cone structure, which is crucial for the low energy excitation. In our calculations, a weakly ordered state with no orbital ordering shows the anisotropy of optical conductivity in accord with experiments. We conclude that the low energy part of the optical conductivity is relevant to the Dirac electron structure rather than the orbital ordering.