Quadrupole Splitting Research Articles

Position and oxidation state of tin in Sn-bearing tetrahedrites Cu12-xSnxSb4S13

We have explored the homogeneity range of Cu12-xSnxSb4S13 tetrahedrites, the peculiarities of their crystal structure, and the oxidation state of tin in them. Phase analysis and crystal structure refinement based on high-resolution powder X-ray diffraction have shown that tin-bearing tetrahedrites exist to the maximum of 0.75÷0.8 tin atoms per formula, with the cubic unit cell parameter increasing from 10.331 to 10.391 Å. The analysis of atomic parameters have proved that tin substitutes for copper only on the Cu(1) site, which is characterized by a regular tetrahedral coordination. The substitution site is further confirmed by 119Sn Mössbauer spectroscopy, showing the low quadrupole splitting, Δ = 0.14–0.16 mm s−1, evidencing the highly-symmetric tetrahedral coordination of tin. Also, the +4 oxidation state of tin directly follows from the isomer shifts values, δ = 1.50–1.52 mm s−1.

Structural insights into the twist-bend nematic phase from the integration of 2H-NMR data and modelling: CB7CB and CB6OCB as case studies

ABSTRACTThe appearance of some special features in 2H-NMR spectra, which could not be explained by the conventional nematic order, was crucial for the discovery of the twist-bend nematic (NTB) phase. Such features reflect the order and symmetry of the local environment of a probe and in principle their analysis can provide quantitative insights into the structural parameters of the phase. We have developed a methodology for the analysis of experimental data, different from the approaches that are normally used for two main reasons: (i) the structural features of the NTB phase, specifically its local polarity, biaxiality and chirality, are consistently taken into account; (ii) the molecular features are introduced in a detailed way, through molecular modelling. We have applied this methodology to analyse 2H-NMR quadrupolar splittings for two representative systems, CB7CB and CB6OCB. The integration of theory, computational modelling and experiment allows us to extract quantitative information from the experimental data and to predict various properties, even not directly probed by measurements. We discuss how the molecular differences between CB7CB and CB6OCB translate into a different phase behaviour and we address issues concerning the distinguishing features of the NTB phase, such as the definition of a local tilted director.

Ab initio study of the role of defects on the magnetic response and the structural, electronic and hyperfine properties of ZnFe2O4

In this work the effects of defects (oxygen vacancies, cationic inversion) on the structural, electronic and the magnetic response of the spinel ZnFe2O4 (ZFO) are studied by using a density functional theory (DFT) based ab initio method (the Full-Potential Linearized Augmented Plane Waves plus Local Orbitals, LAPW+lo) on the framework of the Generalized Gradient Approximation plus U (GGA+U) level. The changes induced by the defects in the hyperfine interactions at the Fe sites of the structure are also presented. In order to discuss the magnetic ordering and the electronic structure of the system we considered different spin arrangements. We found that, similar to the normal and pristine case, reduced and partially inverted ZFO presents an energy landscape characterized by a large number of metastable states. Our calculations successfully describe the hyperfine properties (isomer shift, magnetic hyperfine field and quadrupole splitting) at the Fe sites that are seen by Mössbauer Spectrocopy (MS) at 4 and 300 K, enabling us to characterize the local structure around Fe atoms. Our LAPW+lo predictions also demonstrate the relevance of both oxygen vacancies and antisites (cationic inversion) in the formation of local ferromagnetic coupling between Fe ions, giving rise to a ferrimagnetic ordering in an otherwise antiferromagnetic compound. This results support conclusions based in experimental results obtained in x-ray magnetic circular dichroism and magnetization measurements performed on zinc ferrites with different cation distributions and oxygen vacancy concentrations reported in the literature.

Best of Two Worlds? How MD Simulations of Amphiphilic Helical Peptides in Membranes Can Complement Data from Oriented Solid-State NMR.

The membrane alignment of helical amphiphilic peptides in oriented phospholipid bilayers can be obtained as ensemble and time averages from solid state 2H NMR by fitting the quadrupolar splittings to ideal α-helices. At the same time, molecular dynamics (MD) simulations can provide atomistic insight into peptide-membrane systems. Here, we evaluate the potential of MD simulations to complement the experimental NMR data that is available on three exemplary systems: the natural antimicrobial peptide PGLa and the two designer-made peptides MSI-103 and KIA14, whose sequences were derived from PGLa. Each peptide was simulated for 1 μs in a DMPC lipid bilayer. We calculated from the MD simulations the local angles which define the side chain geometry with respect to the peptide helix. The peptide orientation was then calculated (i) directly from the simulation, (ii) from back-calculated MD-derived NMR splittings, and (iii) from experimental 2H NMR splittings. Our findings are that (1) the membrane orientation and secondary structure of the peptides found in the NMR analysis are generally well reproduced by the simulations; (2) the geometry of the side chains with respect to the helix backbone can deviate significantly from the ideal structure depending on the specific residue, but on average all side chains have the same orientation; and (3) for all of our peptides, the azimuthal rotation angle found from the MD-derived splittings is about 15° smaller than the experimental value.

Magnetic properties of mixed sodium-lithium iron fluorophosphate NaLiFePO4F cathode material

Mixed sodium-lithium iron fluorophosphates NaLiFePO4F was synthesized by solid-state route. The crystal and magnetic properties were investigated by X-ray diffraction (XRD) measurement, vibrating sample magnetometer (VSM), and Mössbauer spectroscopy. The crystal structure of NaLiFePO4F was determined to be orthorhombic with space group of Pnma. The cell parameters of NaLiFePO4F are as follows: a0 = 10.9661 Å, b0 = 6.3693 Å, c0 = 11.4342 Å, and V = 798.6377 Å3. The temperature-dependence of the zero-field-cooled (ZFC) and field-cooled (FC) curves was examined by VSM at 100 Oe from 4.2 to 295 K. We determined the Néel temperature (TN = 22 K) and spin reorientation temperature (TS = 13 K). The Mössbauer spectra of NaLiFePO4F were taken at various temperatures ranging from 4.2 to 295 K. At below TS, the electric quadrupole splitting (ΔEQ) decreased and magnetic hyperfine field (Hhf) increased with decrease temperature due to spin-orbit coupling.

Superconductivity in doped FeTe1−xSx (x = 0.00 to 0.25) single crystals

We report self flux growth and characterization of FeTe1-xSx (x = 0.00 to 0.25) single crystal series. Surface x-ray diffraction (XRD) exhibited crystalline nature with growth in (00l) plane. Micro-structural (electron microscopy) images of representative crystals showed the slab-like morphology and near stoichiometric composition. Powder XRD analysis (Rietveld) of single crystals exhibited tetragonal structure with P4/nmm space group and decreasing a and c lattice parameters with increase in x. Electrical resistivity measurements (ρ-T) showed superconductivity with at 9.5 K and 8.5 K for x = 0.10 and x = 0.25 respectively. The un-doped crystal, i.e., x = 0.00, exhibited known step like anomaly at around 70 K. Upper critical field Hc2(0), as calculated from magneto transport [ρ(T)H], for x = 0.25 crystal is around 60Tesla and 45Tesla in H//ab and H//c directions. Thermal activation energy [U0(H)] calculated for x = 0.10 and 0.25 crystals followed weak power law, indicating single vortex pinning at low fields. Mossbauer spectra for FeTe1-xSx crystals at 300 K and 5 K are compared with non superconducting FeTe. Both quadrupole splitting (QS) and isomer shift (IS) for S doped crystals were found to decrease. Also at 5 K the hyperfine field for x = 0.10 superconducting crystal is decreased substantially from 10.6Tesla (FeTe) to 7.2Tesla. For x = 0.25 crystal, though small quantity of un-reacted Fe is visible at room temperature, but unlike x = 0.10, the low temperature (5 K) ordered FeTe hyperfine field is nearly zero.

Synthesis and magnetic properties of spinel Zn1−xNixFe2O4 (0.0 ≤ x ≤ 1.0) nanoparticles synthesized by microwave combustion method

Nanoparticles of Zn1−xNixFe2O4 (x = 0.0–1.0 in step of 0.2) ferrites are synthesized by microwave combustion method using glycine as a fuel. The structure, site occupancy and ferrimagnetic behavior have been characterized by X-ray diffraction (XRD), Mössbauer Spectroscopy (MS) and Vibrating Sample Magnetometer (VSM). Special emphasis is given to the information provided by each of these techniques concerning the impact of the site occupancy on the magnetic properties. The results reveal the formation of single phase cubic spinel with crystallite sizes in the range of 30–42 nm. The lattice constants and the lattice strains decrease gradually with increasing Ni-content. Two well-defined Mössbauer sextets in the spectra at 78 K belong to octahedral [B] and tetrahedral (A) sites, respectively, confirming the formation of Zn1−xNixFe2O4 spinel. The isomer shift (δFe) values were assigned to Fe3+ ions distributed in both A and B sites. The quadrupole splitting (Δ) values showed also that the orientation of the magnetic hyperfine field (Hint) with respect to the principle axes of the electric field gradient (EFG) is random. The nanosize samples In the presence of an externally applied magnetic field prepared exhibit the hysteresis loops of the ferrimagnetic nature. The value of saturation magnetization increases with introducing Ni up to x = 0.8 and then it decreases. The magnetic data parameters of this structure are discussed as a function of the content of Ni ions.

Spin crossover in two 1D Fe(II) polymers with 1,2,4-triazole thiourea building blocks

The 1D chain [Fe(Etutrz)3](ClO4)2 ⋅ 1.5H2O (2) (Etutrz = 1-ethyl-3-(4H-1,2,4-triazol-4-yl) thiourea), displays pronounced thermochromism with a purple color at 77 K while the sample is white at 300 K. Investigation of magnetic properties reveal an abrupt spin transition around 227 K. Differential scanning calorimetry studies on cooling display a first order phase transition at around 200 K with an entropy variation of ΔS = 61.3 J mol− 1 K− 1. 57Fe Mossbauer spectroscopy of 2 confirms a complete spin transition with a 100% high-spin population at 300 K (isomer shift δHS = 1.04(1) mm/s, quadrupole splitting ΔEQ = 2.86(2) mm/s). The Fe(II) ions convert to the low-spin state at 78K (δLS = 0.53(2) mm/s). The quadrupole splitting, ΔEQ = 0.29(2) mm/s, confirms the presence of distorted octahedra within the 1D chain. The 1D chain [Fe(Etutrz)3](BF4)2 ⋅2MeOH (1) exhibits a different magnetic behavior with a gradual spin conversion at T1/2 = 221 K, whereas thermochromic properties are maintained.

Mössbauer Studies of LixFe1/3Mn1/3Ni1/3PO4 Cathode Materials

We report on the crystallographic and magnetic properties of LixFe1/3Mn1/3Ni1/3 PO4 (x = 0, 1) using x-ray diffraction (XRD), a vibrating sample magne- tometer (VSM), and Mossbauer spectroscopy. XRD analysis confirmed that the samples have an orthorhombic structure with space group Pnma. From the VSM measurements the samples exhibited an antiferromagnetic behavior with a Curie–Weiss temperature θ = − 162 K for x = 1, and θ = − 303 K for x = 0. The Neel temperature (TN) and spin reorientation temperature (TS) were determined to be 40 K and 10 K for x = 1, and 66 K and 25 K for x = 0. The hyperfine field (Hhf) of LiFe1/3Mn1/3Ni1/3PO4 had smaller values than that of Fe1/3Mn1/3Ni1/3PO4 due to the magnitude of the nearest-neighbor superexchange interaction. Isomer shift (δ) values indicate that the charge states of LiFe1/3Mn1/3Ni1/3PO4 are ferrous (Fe2+), and that of Fe1/3Mn1/3Ni1/3PO4 are ferric (Fe3+). The larger values of the electric quadrupole splitting (δEQ) for the Fe2+ phase compared to the Fe3+ phased originated from the different lattice and valence electron contributions due to the crystalline field and valence transition. Debye temperatures (θD) of 338 ± 5 K (x = 1), and 370 ± 5 K (x = 0) were obtained for the samples.

Characterisation of a new nematic lyotropic liquid crystal with natural lipids from soybean

ABSTRACTSearching for a lubricant to be used in articular bone joints, a new nematic liquid crystal (NLC) was characterised. It is formed by dissolving tetradecyltrimethyl ammonium bromide (TTAB), decanol (DeOH), sodium bromide (NaBr) and a natural mixture of lipids (PL, from soybean) in water. Small amounts of DO, and SDS-d were added as2H-NMR probes. The mesophases were characterised using2H-NMR spectroscopy, kinematic viscosity measurements, polarised light microscopy (PLM) and molecular dynamics (MD) simulations. The present system is suitable for lubrication applications, since the solution viscosity is tunable from 49 to 811 cp, more than twice the range previously obtained in a similar system. The solution contains an important proportion of a natural mixture of lipids extracted from soybean, enhancing biocompatibility. The wider range of viscosity displayed by this system, without losing the nematic phase, is attributed to the greater amount of amphiphiles supported by the solution and the size and elongation of the aggregates when the surface charge density is increased. This elongation represents a phase transition from a discotic monoaxial phase to biaxial phase and is responsible for the changes in quadrupolar splittings.

Electrochemical, Spectroelectrochemical, Mößbauer, and EPR Spectroscopic Studies on Ferrocenyl-Substituted Tritylium Dyes.

Four monoferrocenyl tritylium derivatives with donor-substituted (OMe, NMe2 ) aryl rings are reported, along with their spectroscopic and electrochemical properties. All the complexes show a one-electron reduction and a quasi-reversible ferrocene oxidation at a very positive potential. Small quadrupole splittings, ΔEQ , in Mößbauer spectra agree with highly electron-deficient ferrocenes. Comparison of the experimental half-wave potentials for ferrocene oxidation, E1/2 (Fc/Fc+ ), with those estimated from established correlations of E1/2 (Fc/Fc+ ) with ΔEQ indicates that the E1/2 values of the anisyl-substituted congeners FcOMe+ and FcMeOMe+ are affected by Coulombic repulsion between the positive charges at the Fe ion and the neighboring methylium site. Electronic spectra are recorded and interpreted with the aid of quantum chemical calculations. UV/Vis spectroelectrochemical measurements as well as chemical reduction provide insight into the redox-induced color changes upon ferrocene oxidation or upon reduction to the neutral trityl radicals. The neutral radicals reversibly form EPR-silent dimers. This process is studied by temperature-dependent EPR spectroscopy, and thermodynamic data for their dimerization are determined. Experimental and quantum chemical data suggest that the dimers assume classical hexaarylethane structures as opposed to normal or "offset" Jacobson-Nauta-type structures.

Understanding Pyrolyzed Fe-N-C Catalysts By Bridging Density Functional Theory Calculations and Mössbauer Spectroscopy

Platinum group metal-free (PGM-free) catalysts for oxygen reduction are being pursued as a solution for scarcity and cost of catalysts utilizing platinum. Transition metal-nitrogen-carbon (M-N-C) materials are currently the most popular of PGM-free catalysts finding use in low temperature fuel cells. Iron-containing Fe-N-C are being synthesized lately in many variations ranging from atomically dispersed to metallic nano-particles containing types. Despite intense effort, much of the structure of these materials remains unknown and the interpretation of the activity and selectivity data rely on substantial hypothesis-based structural assumptions. 57Mössbauer spectroscopy is gaining significant importance in the experimental characterization of pyrolyzed Fe-N-C catalysts [1]. Isomer shifts and quadrupole splittings (QS), two main features of the 57Mössbauer spectra of Fe-bearing materials, vary systematically as a function of 57Fe oxidation, spin states, and coordination and can be used to accurately determine the local chemical environment of Fe ions in the Fe-N-C materials. All Fe-N-C catalysts have shown at least two clearlydistinct doublets in their Mössbauer spectra, often labeledas D1 and D2. The D1 doublet has an isomer shift value ranging from 0.33 to 0.4 mm/s and quadrupole splitting ranging from 0.7 to 1.2 mm/s, which is usually empirically attributedto Fe-N4defects with Fe2+in its low spin state. The assignment of the D2 doublet with isomer shifts ranging from 0.36 to 0.52 mm/s and with quadrupole splitting ranging from 2.4 to 2.7 mm/s is more ambiguous.It is attributedto Fe-N4 defects similar to iron phthalocyanine with Fe2+in its intermediate spin state or to a Fe-N2+2 defect in which Fe binds to four pyridinic nitrogen atoms from two adjacent nitrogen-doped graphene layers. However, the assignment of these doublets has been basedon experimental reports on carbon-supported FeN4macrocycles, which differs greatly from the case in which the Fe-Nxmoieties are integratedintothe graphene matrix. Therefore, there is a need for combining density functional theory (DFT) calculations of isomer shifts and quadrupole splittings on more realistic models, and compare them to those experimentally extracted with different fitting approaches from the Mössbauer spectraof real Fe-N-C materials. The DFT theory has been applied previously to calculate 57Fe isomeric shifts and quadrupolesplitting for different Fe-containing molecules, but has not yet been appliedtothe Fe-Nxdefects incorporated in the graphene matrix. In this work, both cluster and periodic approacheswere used to calculate thequadrupolesplitting in Fe-N4defects that are identified as the active sites in the pyrolyzed Fe-N-C materials. Because of the well-documented dependence of the DFT computed QS on the exchange-correlation functionals and basis sets [2],the methodology has been first tested for benchmark systems, shown in the Figure. Extensive computations of QS in Fe-N4models with Fe in various coordinationsand with different oxidation/spin states have also been carried out. Furthermore, the DFT calculated values were compared with experimental data to interpret quadrupole doublets ubiquitous in the Mössbauer spectra of pyrolyzed Fe-N-C catalysts. This paper will bring to discussion both computational approaches and correlations of 57Mössbauerspectroscopy “fingerprints” with observed and hypothesized structural motifs of Fe-containing active sites in PGM-free electrocatalysts for oxygen reduction reaction. Zitolo A., Goellner V., Armel V., Sougrati M.-T., Mineva T., Stievano L., Fonda E., Jaouen F., Identification of catalytic sites for oxygen reduction in iron- and nitrogen-doped graphene materials, Nature Materials, 14 , 937 (2015). Pápai M. and Vankó G., On Predicting Mössbauer Parameters of Iron-Containing Molecules with Density-Functional Theory, J. Chemical Theory and Computation, 9, 5004 (2013). Figure 1

Cobalt substituted nickel ferrites via Pechini’s sol–gel citrate route: X-band electromagnetic characterization

Cobalt substituted nickel spinel ferrites were synthesized in the form of Ni1-xCoxFe2O4(x=0-1,Δx=0.15) via Pechini’s sol–gel citrate method with final sintering at 1000 °C for 6 h. Structural purity of the prepared ferrites is examined by using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Thermo-gravimetric and differential thermal analysis (TG-DTA) show that the formation of spinel phase is completed upto 700 °C. Lattice constant, cationic distribution and cationic site parameters are estimated from XRD data. For the first time, lattice parameter (a) is determined using four different methods and quite similar values are obtained in those. Characteristic peaks of nickel ferrites are observed in the Raman spectrum of each ferrite composition. Grain size (80–95 nm) is observed to be higher than crystallite size (26.2–31.8 nm) due to agglomeration of grains. Mössbauer spectra recorded at 300 K temperature show the presence of iron in only +3 valency. Variations of isomer shift, hyperfine field, quadrupole splitting and line width are analyzed with the amount of doped cobalt. This paper also presents the electromagnetic and shielding properties of these Ni–Co ferrites in X-band (8.2–12.4 GHz) frequency range using vector network analyzer (VNA). The analysis of shielding effectiveness shows that increasing the amount of cobalt in nickel ferrites results in increase in shielding efficiency of the ferrites which proves the utility of this specific doping.

How Does a Heme Carbene Differ from Diatomic Ligated (NO, CO, and CN-) Analogues in the Axial Bond?

Compared to well studied diatomic ligands (NO, CN-, CO), the axial bonds of carbene hemes is much less known although its significance in biological chemistry. The unusually large quadrupole splitting (Δ EQ = +2.2 mm·s-1) and asymmetric parameter (η = 0.9) of the five-coordinate heme carbene [Fe(TTP)(CCl2)], which is the largest among all known low spin ferrohemes, has driven investigations by means of Mössbauer effect Nuclear Resonance Vibrational Spectroscopy (NRVS). Three distinct measurements on one single crystal (two in-plane and one out-of-plane) have demonstrated comprehensive vibrational structures including stretch (429) and bending modes (472 cm-1) of the axial Fe-CCl2, and revealed iron vibrational anisotropy in three orthogonal directions for the first time. Frontier orbital analysis especially comparisons with diatomic analogues (NO, CN-, CO) suggest that CCl2, similar to NO, has led to strong but anisotropic π bonding in a ligand-based "4C"-coordinate which induced the vibrational anisotropies and very large Mössbauer parameters. This is contrasted to CN- and CO complexes which possess a porphyrin-based "4N"-coordinate electronic and vibrational structures due to inherent on-axis linear ligation.

Microstructural, Optical, and Magnetic Properties of Vanadium-Substituted Nickel Spinel Nanoferrites

The current study investigates the impact of vanadium substitution on the structural, magnetic, and optical properties of NiFe2−xVxO4 (x ≤ 0.3) nanoparticles (NPs) produced by the cost-effective sol-gel route. The as-prepared spinel ceramic powders were examined by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The functional groups, spinel phase, and crystal structure were confirmed by XRD and FT-IR, respectively. The crystallites size decreased from 45.24 to 36.56 nm as the doping process increases. The plots of Tauc were drawn to determine optical band gap magnitudes of 1.291, 1.302, and 1.312 eV for x = 0.0, 0.2, and 0.3, respectively. The estimated saturation magnetization is maximum for pristine NiFe2O4 NPs and decreases to minimum for NiFe1.7V0.3O4 NPs. The σ-H hysteresis loops have finite coercivity (between 125 and 169 Oe) and retentivity (between 9.36 and 14.04 emu/g) values. The calculated σr/σs ratios are lower than 0.500, assigning the uniaxial anisotropy for NiFe2−xVxO4. The effective anisotropy constants (Keff) are in the range of 0.824 × 105 and 1.303 × 105 Erg/g. The magnetocrystalline anisotropy field (Ha) values are around 5.0 kOe. The characteristics of hysteresis (σ-H) curves and the order of magnetic data reveal the soft ferrimagnetic feature of as-prepared nanoparticle samples. From Mossbauer analysis, the variations in hyperfine magnetic field, quadrupole splitting, line width, and isomer shift have been evaluated. The distribution of cations showed that the octahedral B sites are occupied by all the ions of V3+. Mossbauer spectra are composed of four Zeeman sextets and one doublet.

Mössbauer characterisation of synthetic analogues of the helvite minerals Fe4M4[BeSiO4]6X2 (M = Fe, Mn, Zn; X = S, Se)

We report on this paper on the Mossbauer characterisation of the family of synthetic helvite analogues, Fe4M4[BeSiO4]6X2 (M = Fe, Mn, Zn; X = S, Se). The data show iron to be present as high spin Fe(II) in tetrahedral coordination. The room temperature Mossbauer spectra are composed either by singlets or doublets with small quadrupole splitting values suggesting a small valence contribution at that temperature. From the dependence of the quadrupole splitting with temperature the separation Δ between the two $e_{g}$ orbitals has been estimated. The values of ${\Delta } $ range from 46.3 cm− 1 for the material Fe8[BeSiO4]6S2 to 58.2 cm1 for the material Fe4Zn4[BeSiO4]6S2. The lack of long-range magnetic order observed in the Mossbauer spectra was confirmed by neutron diffraction data which suggests that the M4X units are largely magnetically isolated within their cages leading to a frustrated magnet with no long range interaction for the sulfide species.

The stannides REIr2Sn4 (RE=La, Ce, Pr, Nd, Sm)

Abstract The stannides REIr2Sn4 (RE=La, Ce, Pr, Nd, Sm) were synthesized from the elements by arc melting or by induction melting in sealed niobium containers. They crystallize with the NdRh2Sn4 type structure, space group Pnma. The samples were characterized by powder X-ray diffraction (Guinier technique). Three structures were refined from single-crystal X-ray data: a=1844.5(2), b=450.33(4), c=716.90(6) pm, wR2=0.0323, 1172 F 2 values, 44 variables for LaIr2Sn4, a=1840.08(2), b=448.24(4), c=719.6(1) pm, wR2=0.0215, 1265 F 2 values, 45 variables for Ce1.13Ir2Sn3.87, and a=1880.7(1), b=446.2(1), c=733.0(1) pm, wR2=0.0845, 836 F 2 values, 45 variables for Ce1.68Ir2Sn3.32. The structures consist of three-dimensional [Ir2Sn4] polyanionic networks in which the rare earth atoms fill pentagonal prismatic channels. The striking structural motif concerns the formation of solid solutions RE 1+ x Ir2Sn4− x on the Sn4 sites, which have similar coordination as the RE sites. Temperature dependent magnetic susceptibility measurements revealed diamagnetic behavior for LaIr2Sn4. CeIr2Sn4, PrIr2Sn4 and NdIr2Sn4 show Curie-Weiss paramagnetism while SmIr2Sn4 exhibits typical van Vleck paramagnetism. Antiferromagnetic ground states were observed for CeIr2Sn4 (T N=3.3 K) and SmIr2Sn4 (T N=3.8 K). 119Sn Mössbauer spectra show a close superposition of four sub-spectra which can be distinguished through their isomer shift and the quadrupole splitting parameter.

AC susceptibility and hyperfine interactions of vanadium substituted barium nanohexaferrites

Vanadium ions substituted BaFe12O19 nanohexaferrites, BaFe12-xVxO19 (0.0 ≤x ≤ 0.1), were produced through the sol-gel auto-combustion route. The structure, morphology and the elemental compositions of various products were examined using X–ray powder diffraction, scanning electron microscopy coupled with EDX and EDS elemental mapping. These techniques confirmed the formation of the desired Ba-nanohexaferrite phases. The crystallites size was found to be 55–58 nm range for all products. The magnetic properties of BaFe12-xVxO19 nanohexaferrites were investigated by Mossbauer spectroscopy, ZFC-FC magnetizations and AC susceptibility. The evolutions in the values of hyperfine magnetic field, isomer shift, quadrupole splitting, and line width were deduced via Mossbauer analysis. The experiments of ZFC and FC magnetizations indicated that no blocking temperature is observed in the temperature interval 2–400 K, which signals the typical ferromagnetic (FM) behavior for the produced nanohexaferrites. A super-spin glass like behavior is noticed at lower temperatures. The experiments AC susceptibility confirmed that the strength of magnetic interactions is enhanced for lower content of V3+ (x = 0.02). For higher amount of V3+, the magnetic interactions are weakened. The obtained results are mainly accredited to the substitutions of Fe3+ ions by V3+ ions.

Role of Ce substitution in the magneto-crystalline anisotropy of tetragonal ZrFe10Si2

We report the study of Zr1-xCexFe10Si2 (x = 0.0, 0.3 and 0.6) compounds, with tetragonal ThMn12 structure, by means of neutron diffraction and Mössbauer spectroscopy to understand the role of Ce in the increasing magneto-crystalline anisotropy. Fitting of the 57Fe Mössbauer spectra to the three Fe atomic positions, namely 8i, 8j and 8f, indicate that Ce displaces Fe from the 8i to the 8j positions and in parallel increases the quadrupole splitting (QS) in position 8f, correlating with the increase of the magneto-crystalline anisotropy. However, the hyperfine field Bhf remains constant for all Ce substitutions. The full occupancy of the 8j positions by Fe at Ce = 0.6 can explain the instability of the ThMn12 structure for similar and higher Ce concentrations. Neutron diffraction experiments show the evolution of the magnetic moment and crystal structure as a function of temperature, showing Ce to cause an increase of the lattice parameters and tetragonal distortion. A large anomaly of the expansion coefficient, due to the spontaneous magnetostriction, is also disclosed. These results support a pure geometric influence of Ce on the magneto-crystalline anisotropy through a selective distortion of the lattice.

Magneto Optical Properties and Hyperfine Interactions of Cr3+ Ion Substituted Copper Ferrite Nanoparticles

Spinel CuCrxFe2−xO4 (0.0 ≤ y ≤ 1.0) nanoparticles were fabricated by co-precipitation. X-ray diffraction proved the pureness and cubic crystal assembly of products which have the crystallite sizes varying between 16 and 33 nm. The cubic morphology and expected chemical composition, spectral analyses of all sample were accomplished via Scanning electron microscopy along with Energy Dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy respectively. Magnetic and optical characterization of samples were done via Vibrating sample magnetometer, Mossbauer spectroscopy and Diffuse reflectance spectroscopy. Kubelka–Munk model was applied to UV–Vis data for calculating the optical Eg (band gap) values between minimum 1.20 and maximum 1.80 eV. Mossbauer analysis determined the consequence of Cr3+ substitution on isomer shift and quadrupole splitting of all products etc. The specific magnetization (σ-H) hysteresis curves have finite coercivity (in a range of 35–410 Oe) and retentivity (in a range of 0.33–3.84 emu/g) values and reveal the soft ferrimagnetic nature of spinel CuCryFe2−yO4 nanoparticles (NPs). The estimated saturation magnetization Ms value of 35.17 emu/g is maximum for pristine CuFe2O4 NPs and decreases to minimum value of 1.57 emu/g for CuCr0.4Fe1.6O4 NPs due to Cr3+ ion substitution. The calculated squareness ratios less than 0.5 assign the uniaxial anisotropy for all CuCryFe2−yO4 NPs. The magneto-crystalline anisotropy field (Ha) values less than 10.0 kOe except for the composition of CuCr0.2Fe1.8O4 NPs are other magnetic data to reveal the soft magnetic character of samples.