Hyperfine Interaction Parameters Research Articles

Absence of the stripe antiferromagnetic order in the new 30 K superconductor ThFeAsN

We report the results of X-ray diffraction and 57Fe Mössbauer spectroscopy study, complemented by ab-initio calculations of the electronic structure, hyperfine-interaction parameters, and elastic properties of the new 30 K superconductor ThFeAsN. The superconductor crystallizes in the tetragonal space group P4/nmm with the lattice parameters a = 4.0356(1) Å and c = 8.5286(1) Å. Contrary to the claims in the literature, we demonstrate unequivocally that there is no magnetic order of the Fe magnetic moments down to 2.0 K. It is suggested that the absence of Fe magnetism may be due to an internal uniaxial chemical pressure whose presence is manifested by the unusually small c/a ratio. Evidence is provided for the presence of a mixture of ionic and covalent chemical bonding and of metallic characteristics. A detailed analysis of the energy band structure of ThFeAsN is presented. The shape of the Mössbauer spectra is accounted for by a quadrupole doublet with a small quadrupole splitting that increases with decreasing temperature. Excellent agreement between the calculated and measured 0 K quadrupole splittings is observed. Fair agreement between the experimental Debye temperature of 332(2) K and the calculated one of 370 K is observed.

Composition-driven structural and magnetic transitions in mechanically activated (1− x )BiFeO 3 –( x )BaTiO 3 solid solutions

Abstract This work presents systematic investigations of the structure and magnetic properties of mechanically activated (1− x )BiFeO 3 –( x )BaTiO 3 solid solutions in a wide range of constituents concentration (x=0.1–0.9). X-ray diffraction and Mossbauer spectroscopy were used as complementary methods in order to control the mechanical activation process and to follow composition-driven structural transition from rhombohedral to cubic symmetry. The investigations revealed that the structural transformation proceeds for x =0.4 and is accompanied by the disappearance of magnetic ordering in the samples. Moreover, evolution of the hyperfine interactions parameters with composition of the solid solutions was discussed in details. In particular, it was shown that hyperfine magnetic field induction decreases due to decreasing energy of superexchange interaction of iron ions. For the paramagnetic samples with x ≥0.4 gradual decrease of quadrupole splitting was detected. Scanning electron microscopy was used to analyze microstructure of the samples and showed that the average grain size is in the range of 200–300 nm.

Aminoxyl Radicals of B/P Frustrated Lewis Pairs: Refinement of the Spin-Hamiltonian Parameters by Field- and Temperature-Dependent Pulsed EPR Spectroscopy.

Q-band and X-band pulsed electron paramagnetic resonance spectroscopic methods (EPR) in the solid state were employed to refine the parameters characterizing the anisotropic interactions present in six nitroxide radicals prepared by N,N addition of NO to various borane-phosphane frustrated Lewis pairs (FLPs). The EPR spectra are characterized by the g-anisotropy as well as by nuclear hyperfine coupling between the unpaired electron and the 11B/10B, 14N and 31P nuclear magnetic moments. It was previously shown that continuous-wave spectra measured at X-band frequency (9.5 GHz) are dominated by the magnetic hyperfine coupling to 14N and 31P, whereas the g-tensor values and the 11B hyperfine coupling parameters cannot be refined with high precision from lineshape fitting. On the other hand, the X-band electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectra are completely dominated by the nuclear hyperfine coupling to the 11B nuclei, allowing a selective determination of their interaction parameters. In the present work this analysis has been further validated by temperature dependent ESEEM measurements. In addition, pulsed EPR data measured in the Q-band (34 GHz) are reported, which present an entirely different situation: the g-tensor components can be measured with much higher precision, and the ESEEM and HYSCORE spectra contain information about all of the 10B, 11B, 14N and 31P hyperfine interaction parameters. Based on these new results, we report here high-accuracy and precision data of the EPR spin Hamiltonian parameters measured on six FLP-NO radical species embedded in their corresponding hydroxylamine host structures. While the ESEEM spectra at Q-band frequency turn out to be very complex (due to the multinuclear contribution to the overall signal) in the HYSCORE experiment the extension over two dimensions renders a better discrimination between the different nuclear species, and the signals arising from hyperfine coupling to 10B, 11B, 14N and 31P nuclei can be individually analyzed.

Lattice dynamics, phase transitions and spin relaxation in [Fe(C5H5)2] PF6

The organometallic compound ferrocenium hexafluorophosphate, [Fe(C5H5)2] PF6, has been studied by Mossbauer spectroscopy in the past, mainly to determine the crystal structure at high temperatures. Here we present studies at 95 K to 305 K and analyze the spectra in terms of spin relaxation theory which yields accurately the hyperfine interaction parameters and the spin-spin and spin-lattice relaxation rates in this paramagnetic compound. The spectral area under the resonance curve yields the recoil free fraction and thus the mean square of the vibration amplitude . One observes a large discontinuity in the slope of versus T at ˜210 K, indicative of a phase transition. The analysis of the spectra proves that the quadrupole interaction is small but certainly negative, ½e2qQ = -0.12(2) mm/s, and causes the asymmetry observed in the spectra. The detailed analysis yields also, for the first time, the fluctuating effective magnetic hyperfine field, H eff = 180(50) kOe.

Coexistence of site- and bond-centered electron localization in the high-pressure phase ofLuFe2O4

Magnetic-electronic hyperfine interaction parameters of spectral components are obtained from in situ $^{57}\mathrm{Fe}$ M\ossbauer spectroscopy pressure studies of the mixed-valence $\mathrm{LuF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ multiferroic, up to $\ensuremath{\sim}30\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and on recovered high-pressure phase samples. Temperature-dependent M\ossbauer spectra of the low-pressure phase show that $\mathrm{F}{\mathrm{e}}^{2+}$ and $\mathrm{F}{\mathrm{e}}^{3+}$ sites are discernible, consistent with known site-centered charge order in the triangular (frustrated) Fe sublattice network. Magnetic spectra of the high-pressure phase, stabilized in a rectangular Fe sublattice network at $Pg8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, exhibit fingerprints of iron in an intermediate valence state only. Temperature-dependent resistivity pressure studies evidence thermally activated small polaron motion in the high-pressure phase. These experimental signatures, complemented by ab initio calculations of electronic structure, are considered evidence of asymmetric dimer formation ${\mathrm{Fe}}^{(2+\mathrm{\ensuremath{\Delta}}+)}\ensuremath{\Leftrightarrow}{\mathrm{Fe}}^{(3\ensuremath{-}\mathrm{\ensuremath{\Delta}})+}$, where the minority-spin electron deconfinement coefficient is $\mathrm{\ensuremath{\Delta}}=0.3\ensuremath{-}0.4$. Bragg satellites discerned in electron diffraction patterns of the metastable high-pressure phase possibly stem from this admixture of site- and bond-centered localization (intermediate-state charge order) in a magnetic background. This breaks inversion symmetry and potentially renders $\mathrm{LuF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ in its high-pressure phase as a new charge order instigated (electronic) ferroelectric.

5 7 Fe Mössbauer spectroscopic studies of single-crystalline K x Fe2-y S 2 and K x Fe2-y Se 2

We have investigated the physical properties of single-crystalline KxFe2-yS2 and KxFe2-ySe2 samples using 57Fe Mossbauer spectroscopy. The observed 57Fe Mossbauer spectra were reconstructed using a major antiferromagnetic ordered K2Fe4Se5 phase and a minor paramagnetic phase down to 5 K, despite being superconducting below 32.2 K in KxFe2-ySe2. The analysis of 57Fe Mossbauer spectrum for KxFe2-yS2 at 290 K confirms the presence of a major antiferromagnetic ordered K2Fe4S5 phase and a minor paramagnetic phase in the KxFe2-yS2 single crystal. The derived hyperfine interaction parameters of the paramagnetic phase in KxFe2-yS2 suggest that the microstructure of this phase in KxFe2-yS2 is similar to that of the superconducting phase in KxFe2-ySe2 although the KxFe2-yS2 single crystals exhibit no superconductivity down to 5 K.

Specific features of magnetic states of impurity iron ions in the perovskite La0.75Sr0.25Co0.98 57Fe0.02O3

Single-phase polycrystalline La0.75Sr0.25Co0.9857Fe0.02O3 samples have been prepared by solidstate ceramic technology. The samples have the rhombohedral structure (space group \(R\bar 3c\)). The studies of perovskite La0.75Sr0.25Co0.9857Fe0.02O3 by Mossbauer spectroscopy on impurity 57Fe nuclei in the temperature range of 5–293 K have revealed the existence of a superparamagnetic relaxation in the temperature range of 100–210 K. The parameters of hyperfine interactions (hyperfine magnetic fields, line shifts, and quadrupole shifts) and the anisotropy energy have been measured, and the frequencies of magnetic moment relaxation of iron ions have been estimated.

An overview of first-principles calculations of NMR parameters for paramagnetic materials

Many technologically important materials exhibit paramagnetism, for example, lithium intercalation materials for lithium-ion batteries and platinum nanoparticles for catalysis. In order to study their properties, for example, their electron transport properties or catalytic efficiency, and hence tailor them to specific engineering applications, information on their structure and bonding needs to be acquired. Solid state nuclear magnetic resonance (NMR) is an excellent experimental method for achieving this; however, the resulting spectra are often difficult to interpret. Calculations based on quantum mechanics therefore provide an invaluable aid for decoding these experimental spectra.The dominant interaction in paramagnetic materials is the hyperfine interaction. This is the interaction between the spin of a nucleus and the spin of an unpaired electron. The hyperfine interaction affects the appearance of NMR spectra, both by shifting the frequencies at which resonance occurs and by removing degeneracies so that a single resonance frequency splits into several frequencies. This review examines the methods and current limitations for calculating hyperfine interaction parameters, placing this in the context of experimental NMR investigations for lithium intercalation materials and platinum nanoparticles. In this way, the importance of developing increasingly accurate methods for calculating hyperfine parameters is illustrated.

Mössbauer spectroscopy, magnetic, and ab-initio study of the approximant Al76Ni9Fe15 to a decagonal Al–Ni–Fe quasicrystal

The structural, magnetic, and Mössbauer spectral properties of the approximant Al76Ni9Fe15 to a decagonal Al–Ni–Fe quasicrystal, complemented by ab-initio electronic structure and the hyperfine-interaction parameters calculations, are reported. The approximant studied crystallizes in the monoclinic space group C2/m with the lattice parameters a = 15.3898(3) Å, b = 8.0840(2) Å, c = 12.4169(2) Å, and β = 107.870(2)∘. The existence of a pseudogap in the calculated electronic density of states slightly above the Fermi level suggests electronic stabilization according to the Hume-Rothery-type mechanism. High metallicity of Al76Ni9Fe15 is predicted. Both the Mössbauer spectra and magnetic susceptibility data indicate that Al76Ni9Fe15 is a paramagnet down to 2.0 K. The presence of the distribution of the electric quadrupole splitting in the Mössbauer spectra measured in the temperature range 4.5–296.1 K is observed. The increase of the average quadrupole splitting with decreasing temperature is well described by a T3/2 power-law relation. The Debye temperature of Al76Ni9Fe15 is found to be 431(3) K.

A detailed study on the transition from the blocked to the superparamagnetic state of reduction-precipitated iron oxide nanoparticles

Magnetic iron oxide nanoparticles were prepared by salt-assisted solid-state chemical precipitation method with alternating fractions of the ferric iron content. The physical properties of the precipitated nanoparticles mainly consisting of magnetite were investigated by means of transmission electron microscopy, high energy X-ray diffraction, vibrating sample magnetometry and Mössbauer spectroscopy. With particle sizes ranging from 16.3nm to 2.1nm, a gradual transition from the blocked state to the superparamagnetic state was observed. The transition was described as a dependence of the ferric iron content used during the precipitation. Composition, mean particle size, coercivity, saturation polarisation, as well as hyperfine interaction parameters and their evolution were studied systematically over the whole series of iron oxide nanoparticles.

Structural phase transformation of as-prepared Mg–Mn nanoferrites by annealing temperature

As-prepared Mg0.2Mn0.8Fe2O4 nanoferrite samples by coprecipitation method were annealed at different temperatures T. XRD, TEM, IR, VSM and Mössbauer techniques were used to characterize the samples. This study proved the transformation of the sample structure from cubic spinel to Z-type hexagonal phase at 700°C. This transformation was assigned to Jahn–Teller effect of the Mn3+ and Fe2+ ions and/or atomic disorder in the crystal lattice. All the deduced structural parameters were affected by the transformation process. The infrared and structural parameters showed dependence on T, whereas tetrahedral band position did not. TEM images showed agglomeration of the nanoparticles, where the average particle size ranged 25–55nm and was a little higher than R. Study on the elastic properties proved the weakening of inter-atomic bonds inside the crystal lattice as T increases. The magnetic properties were affected by the transformation process and showed T dependence, whereas Ms and Hc proved dependence on porosity. Hyperfine interaction parameters, area ratio (B/A) and spontaneous magnetization were discussed as functions of T.

Exchange coupled L10-FePt/fcc-FePt nanomagnets: Synthesis, characterization and magnetic properties

We report synthesis, characterization and magnetic properties of exchange-coupled L10-FePt/fcc-FePt nanomagnets. Structural and morphological characterization of exchange-coupled L10-FePt/fcc-FePt was carried out by powder X-ray diffraction, Mössbauer spectroscopy and transmission electron microscopy. Rietveld refinement of powder X-ray diffraction pattern has been used to quantify L10-FePt and fcc-FePt phases present in samples. Room temperature Mössbauer spectroscopy showed sextets of both L10-FePt and fcc-FePt phases with their respective hyperfine interaction parameters. Transmission electron microscopic (TEM and HRTEM) images confirmed nanocrystalline nature of exchange-coupled nanomagnets with particle size ranges from 15nm to 50nm after annealing for different time at 700°C. Room temperature magnetic studies showed ferromagnetic nature of nanomagnets and maximum energy product (BH)max~10.92 MGOe was obtained for sample containing 89.0% volume fraction of L10-FePt phase.

Search for Fe magnetic ordering in the 40 K superconductor (Li0.8 Fe0.2)OHFeSe

We report the results of x-ray diffraction and 57 Fe Mössbauer spectroscopy study, complemented by ab-initio electronic structure and the hyperfine-interaction parameters calculations, of the 40 K superconductor (Li0.8 Fe0.2)OHFeSe. The superconductor crystallizes in the tetragonal space group P4/nmm with the lattice constants a = 3.7865(2) Å and c = 9.2802(6) Å. Evidence is provided for the presence of an anisotropic mixture of strong covalent and weak ionic chemical bonding and of metallic characteristics. The Mössbauer spectra consist of two quadrupole-doublet patterns corresponding to Fe2+ at the 2a and 2b sites. Contrary to the claims in the literature, we demonstrate unequivocally that there is no magnetic ordering of the 2a-site Fe magnetic moments down to 2.0 K. The calculated hyperfine-interaction parameters at the two Fe sites show general agreement with the experimental ones. The Debye temperatures for the 2a and 2b sites are found to be 186(21) and 397(4) K, respectively.

Mössbauer spectroscopy, magnetic, and ab initio study of the Heusler compound Fe2NiGa

The structural, electronic, magnetic, elastic, and hyperfine-interaction properties of Fe2NiGa have been determined by means of X-ray diffraction, 57Fe Mössbauer spectroscopy, and magnetic measurements and ab initio calculations. The compound studied crystallizes in the cubic space group F4¯3m with lattice constant a=5.7961(4)A˚. Evidence is provided for the presence of significant structural disorder in the compound. Fe2NiGa is predicted to be half-metallic with covalent chemical bonding. It orders ferromagnetically with the Curie temperature TC=586.0(7)K. The saturation magnetization per formula unit and the estimated Fe magnetic moments at the A and B sites are 3.00, 1.87(2), and 2.25(2) μB, respectively. The ab initio calculations overestimate the values of the A- and B-site Fe magnetic moments. It is observed that the magnetic properties of Fe2NiGa are very strongly dependent on its heat treatment. The calculated hyperfine-interaction parameters show general agreement with the experimental ones. It is demonstrated that the compound studied decomposes when heated and kept at temperatures above around 500K. The Debye temperature of Fe2NiGa is found to be 378(5)K.

Mössbauer studies of the formation of Cr-doped cementite during mechanochemical synthesis and subsequent annealings

The structure, parameters of hyperfine interactions, and localization of Cr atoms in mechanically alloyed and annealed cement (Cr-doped compounds (Fe1–XCrX)3C, where X = (0.01–0.10)) are studied by means of Mossbauer spectroscopy, X-ray diffraction, and magnetic measurements. It is shown that the distribution of Cr atoms in annealed cementite is quite close to statistically homogeneous.

Hyperfine interactions of 57Fe impurity nuclei in multiferroic CuCrO2

Hyperfine interactions of 57Fe nuclei in multiferroic CuCrO2 are studied by means of Mossbauer probe spectroscopy in a wide range of temperatures, including that of the magnetic phase transition. The temperature dependences of the parameters of electric and magnetic hyperfine interactions and the anharmonicity parameter of the spin wave are obtained as part of the spatial anharmonic spin-modulated structure.

Mössbauer spectrocopy in the technology of nanocomposite functional materials

Research results obtained to date by applying Mossbauer spectroscopy to iron-containing nanosized structures and the revealed patterns of how the nanoscale state impacts hyperfine interaction parameters in simple, multicomponent, and hybrid systems lay the groundwork for developing algorithms for the targeted synthesis of multifunctional nanoscale materials. This work discusses the contribution Mossbauer spectroscopy is making to the development of technologies for synthesizing new functional nanocomposites containing mechanically activated nanoparticles.

Mössbauer spectroscopy study of a new layered iron oxyselenide Na2Fe2Se2O

We report the results of 57Fe Mössbauer spectroscopy study, complemented by first-principles energy-band structure and the hyperfine-interaction parameters calculations, of a recently discovered layered iron oxyselenide Na2Fe2Se2O. It is confirmed that Na2Fe2Se2O is a Mott insulator. It is demonstrated experimentally that Na2Fe2Se2O orders antiferromagnetically with the Néel temperature TN=74.8(2)K and with the Fe magnetic moment of 3.0(1)μB. The calculated hyperfine-interaction parameters are in good agreement with the corresponding experimental parameters. The Debye temperature of Na2Fe2Se2O is found to be 274(3)K.

Two-dimensional HYSCORE spectroscopy of superoxidized manganese catalase: a model for the oxygen-evolving complex of photosystem II.

The solar water-splitting protein complex, photosystem II (PSII), catalyzes one of the most energetically demanding reactions in Nature by using light energy to drive a catalyst capable of oxidizing water. The water oxidation reaction takes place at the tetra-nuclear manganese calcium-oxo (Mn4Ca-oxo) cluster at the heart of the oxygen-evolving complex (OEC) of PSII. Previous studies have determined the magnetic interactions between the paramagnetic Mn4Ca-oxo cluster and its environment in the S2 state of the OEC. The assignments for the electron-nuclear magnetic interactions that were observed in these studies were facilitated by the use of synthetic dimanganese di-μ-oxo complexes. However, there is an immense need to understand the effects of the protein environment on the coordination geometry of the Mn4Ca-oxo cluster in the OEC of PSII. In the present study, we use a proteinaceous model system to examine the protein ligands that are coordinated to the dimanganese catalytic center of manganese catalase from Lactobacillus plantarum. We utilize two-dimensional hyperfine sublevel correlation (2D HYSCORE) spectroscopy to detect the weak magnetic interactions of the paramagnetic dinuclear manganese catalytic center of superoxidized manganese catalase with the nitrogen and proton atoms of the surrounding protein environment. We obtain a complete set of hyperfine interaction parameters for the protons of a water molecule that is directly coordinated to the dinuclear manganese center. We also obtain a complete set of hyperfine and quadrupolar interaction parameters for two histidine ligands as well as a coordinated azide ligand, in azide-treated superoxidized manganese catalase. On the basis of the values of the hyperfine interaction parameters of the dimanganese model, manganese catalase, and those of the S2 state of the OEC of PSII, for the first time, we discuss the impact of a proteinaceous environment on the coordination geometry of multinuclear manganese clusters.

Characterization, structural and magnetic properties of the as-prepared Mg-substituted Cu-nanoferrites

The as-prepared Cu1−xMgxFe2O4 nanoferrites, 0⩽x⩽1, were synthesized using the co-precipitation method. The samples were characterized using the X-ray diffraction, transmission electron microscopy, infrared (IR) and Mössbauer spectroscopy and vibrating sample magnetometer. This study proved that the samples have single-phase cubic spinel structure, nanometric size and superparamagnetic behavior. The nanoparticle and crystallite size (R) showed a dependence on the Mg ion content x. The Mössbauer spectra were analyzed and assigned to two magnetic subpatterns and/or two quadrupole doublets due to Fe ions among the tetrahedral A-sites and octahedral B-sites. Six IR absorption bands were observed and assigned to the corresponding vibration modes. The saturation magnetization showed decrease against x and proved dependence on R. The lattice constant, hopping lengths, strain, site characteristic bands and B-site force constant showed x dependence, whereas oxygen parameter and A-site force constant did not. The site ionic radii and edges, density, porosity, Debye temperature, stiffness constant, hyperfine interaction and magnetic parameters were deduced and discussed as functions of x and the cation distributions were estimated.