Magnetic Hyperfine Splitting Research Articles

Laser site-selective spectroscopy and magnetic hyperfine splittings of Ho3+ doped Y2SiO5

Laser site-selective spectroscopy and high-resolution absorption measurements have been used to determine 51 crystal-field energy levels for one of the Ho3+ centres in Y2SiO5. This centre is denoted as Site 2 and has been tentatively assigned as the seven-fold coordinated centre. High resolution absorption measurements reveal complex hyperfine patterns that obey an approximate selection rule. The application of a magnetic field along the three optical axes reveals the presence of avoided crossings below 0.5 Tesla, in both the ground and excited states.

Effect of La substitution on the structural and chemical properties of Barium hexaferrite via Mossbauer spectroscopy

M-type Barium hexaferrite is a famous hard magnetic material with a hexagonal crystal structure. La substituted Barium hexaferrite, Ba(1-x)La(x)Fe12O19, (where, x = 0.25 and 0.30) were synthesized using ball milling followed by sintering at 1300 °C for 5 hours. X-ray diffraction patterns reveal the formation of a single-phase magnetoplumbite structure of barium hexaferrite, which belongs to the P63/mmc space group. Mossbauer spectroscopic studies were carried out to study the magnetic phase, the effect of La doping on the valency of the Fe atom, and charge distribution in the prepared samples. Mossbauer spectra is fitted using 5 sextets, shows there is 5 sublattices present in the system. From the fitting of Mossbauer spectrum, it is observed that, there is no formation of Fe2+ ion even if the doping levels are as high as 30%, as it is expected that Fe3+ ion changes its valance to maintain the charge neutrality. However, there is an increase in s-electron density for number of sites with doping. Quadrupole splitting values shows spherical charge distribution for all the sublattices except 2b, due to asymmetric nature of bipyramidal site. Slightly varied magnetic hyperfine splitting values are observed for 12 k and 4f1 sites shows the effect of La substitution.

Investigation of Mn-Fe magnetic interaction in mechanically alloyed Fe doped-MnAlC by 57Fe Mössbauer spectrometry

Four samples γ2-Mn40Fe0.5Al59.5, β-Mn60Fe0.5Al39.5, and ε-Mn50.5Fe0.5Al47C2, τ-Mn50.5Fe0.5Al47C2 were synthesized by mechanical alloying method. X-ray diffraction results showed high purity of the γ2, β, ε, and τ phases in each sample. Mössbauer measurement at room temperature showed non-ferromagnetic characteristic of the γ2-Mn40Fe0.5Al59.5, β-Mn60Fe0.5Al39.5, and ε-Mn50.5Fe0.5Al47C2. Interestingly, τ-Mn50.5Fe0.5Al47C2 showed a complex magnetic hyperfine splitting, indicating magnetic ordered structure. The hyperfine interaction in τ-Mn50.5Fe0.5Al47C2 was found dependent with temperature, in which isomer shift (IS) and magnetic hyperfine field (Bhf) decreased with increasing temperature. From the IS temperature dependence curve, the Debye temperature (θD) is determined to be 422 ± 80 K. The temperature dependence of Bhf values and the thermomagnetic measurement yielded a Curie temperature (Tc) values of 560 ± 13 K and 565 ± 2 K respectively. In order to investigate the magnetic interaction between Fe and Mn atoms in τ-Mn50.5Fe0.5Al47C2, local magnetic order of τ-Mn50.5Fe0.5Al47C2 was probed by using in-field 57Fe Mössbauer spectrometry. The obtained results showed that Fe and Mn formed a non-collinear magnetic structure with magnetic moments of Fe at different sites showing different canting angles with neighboring Mn atoms.

Storage and manipulation of single x-ray photons via nuclear hyperfine splitting

We introduce a technique to store and manipulate single x-ray photons, which relies on dynamically controlled absorption via nuclear hyperfine magnetic splitting. This scheme is inherently suitable for storage, on-demand generation, and dynamical manipulation of single x-ray photons, for instance, the manipulation of the temporal shape, temporal splitting, the interference between x-ray photons, and the control of the polarization. Our approach provides more opportunities in x-ray quantum information.

Crystal structure and magnetic properties in semiconducting Eu3−δZnxSnyAs3 with Eu-Eu dimers

Magnetic structure and crystal symmetry, which primarily determine the time-reversal and inversion symmetry, may give rise to numerous exotic quantum phenomena in magnetic semiconductors and semimetals when arranged in different patterns. In this work, a new layered magnetic semiconductor, Eu3−δZnxSnyAs3, was discovered and high-quality single crystals were grown using the Sn flux. According to structural characterization by x-ray diffraction and atomic-resolution scanning transmission electron microscopy, Eu3−δZnxSnyAs3 is found to crystallize in a hexagonal symmetry with the space group P63/mmc (No. 194). After examining different specimens, we conclude that their stoichiometry is fixed at ∼Eu2.6Zn0.65Sn0.85As3, which meets the chemical charge balance. Eu3−δZnxSnyAs3 is composed of septuple (Eu1−δSnyAs2)-Eu-(ZnxAs)-Eu sequences. The shortest Eu–Eu distance in the system is between two Eu layers separated by ZnxAs along the c-axis. Magnetization measurement shows an antiferromagnetic ordering in Eu3−δZnxSnyAs3 at TN ∼ 12 K, where the magnetic easy-axis is along the c-axis, and Mössbauer spectroscopy observes magnetic hyperfine splitting on Eu and Sn at 6 K. Magnetic anisotropy is significantly different from the ones along the ab-plane in other layered Eu-based magnetic semimetals. Heat capacity measurements confirm the magnetic transition around 12 K. Electrical resistivity measurement indicates semiconductor behavior with a band gap of ∼0.86 eV. Various Eu-based magnetic semiconductors could provide a tunable platform to study potential topological and magnetic properties.

Structural, Physical, Theoretical and Spectroscopic Investigations of Mixed‐Valent Eu2Ni8Si3 and Its Structural Anti‐Type Sr2Pt3Al8

AbstractEu2Ni8Si3 and its anti‐type representative Sr2Pt3Al8 were synthesized from the elements. They crystallize in the tetragonal crystal system with space group P42/nmc and with lattice parameters of a=997.9(1) and c=747.6(1) pm (Eu2Ni8Si3) as well as a=1082.9(2) and c=823.3(2) pm (Sr2Pt3Al8). Both compounds were investigated via single crystal X‐ray diffraction, indicating slight Si/Ni mixing for the silicide. Sr2Pt3Al8 exhibits a temperature independent magnetic susceptibility, suggesting superimposed dia‐ and Pauli‐paramagnetic contributions. The independent Al and Pt sites of the platinide were further characterized by 27Al and 195Pt solid‐state NMR spectroscopy, which were assigned with the help of electronic structure calculations. ICOHP calculations and Bader charges were used to analyze the bonding situation. Eu2Ni8Si3 in contrast is paramagnetic with a ferromagnetic transition at TC=46.9(2) K and exhibits an effective magnetic moment of μeff=6.61(1) μB per Eu atom. The latter is in line with an intermediate valence that was further proven by 151Eu Mößbauer spectroscopic investigations. At 300 K, the refined Eu2+/Eu3+ ratios are 60 %/40 %, at 78 K 62 % and 38 % (Eu2+/Eu3+) are observed, being in line with the ratio deduced from the magnetic susceptibility. Finally, at 6 K a ratio of 68 % Eu2+ and 32 % Eu3+ was observed. Below the Curie temperature, the Eu2+ signal shows a full magnetic hyperfine splitting, with an internal magnetic field value of B0=28.4 T.

M\xf6ssbauer and Raman characterization of ash produced by burning ancient buried Japanese cedar and investigation for its unusual color tone

Mössbauer and Raman spectroscopic characterization of colored ash samples made by combustion of ancient buried Japanese cedar (Cryptomeria japonica) was carried out, and the factors governing the color tones were investigated mainly in terms of the chemical species of Fe. The ash samples displayed various unusual colors, depending clearly on the individual ancient tree and the part of it. Some of Mössbauer spectra of the ash samples showed magnetic hyperfine splittings due to internal magnetic fields. The Mössbauer and Raman spectra suggested that the primary Fe-containing species in all the ash samples was calcium ferrite, Ca2Fe2O5.

Microstructural and magnetic properties of electrospun hematite/cuprospinel composites

Phase composition, microstructural and magnetic properties of electrospun hematite/cuprospinel composites were investigated. Samples were synthesized starting with 0 to 10 mol% of copper relative to iron. The round shape of reference electrospun fibres was preserved upon their heating up to 600 °C in air, whereas at 700 °C hollow substructure was additionally formed. In these reference samples the presence of hematite phase was detected by XRPD. A small amount (traces) of Fe3O4/γ-Fe2O3 was also found, due to the reduction conditions created during the burning of the polyvinylpyrrolidone matrix. Rietveld analysis of samples containing 10 mol% copper and produced at 500 °C and 700 °C did not show the tendency to form solid solutions between hematite and Cu cations. Electrospun fibres containing 10 mol% copper after heating at 500 °C consisted of magnetite and cubic cuprospinel as the dominant phases and hematite as the associated phase. Upon heating at 700 °C the phase composition showed the presence of hematite as the dominant phase and tetragonal cuprospinel as the associated phase. For this tetragonal cuprospinel the formula Cu0.6Fe2.4O4 was calculated. Mossbauer spectra recorded at 20 °C and at liquid helium temperature also showed the presence of hematite and spinel structures. Measured hyperfine magnetic splitting reflected the distributions of Fe2+, Fe3+ and Cu2+ cations in the spinel structures. The magnetic measurements also confirmed that there is no Cu incorporation into the electrospun hematite.

New insight on the Mössbauer spectra for Fe16N2 thin films with high saturation magnetization

Mössbauer spectroscopy was conducted on partially ordered Fe16N2 thin films. Besides the dominant polarized core-s electron Fermi contact term, valence electron contribution was counted as a necessity for the explanation of a combination of a high magnetic moment and a relatively low magnetic hyperfine splitting, which were obtained on Fe16N2 thin films with both GaAs and MgO substrates. Essentially, the “cluster + atom” model was applied to understand the high degree hybridization of s–p–d electron, which allows the increase of the positive valence electron contribution and the decrease of the total hyperfine field.

Synthesis and Characterization of Sodium-Iron Antimonate Na2FeSbO5: One-Dimensional Antiferromagnetic Chain Compound with a Spin-Glass Ground State.

A new oxide, sodium-iron antimonate, Na2FeSbO5, was synthesized and structurally characterized, and its static and dynamic magnetic properties were comprehensively studied both experimentally by dc and ac magnetic susceptibility, magnetization, specific heat, electron spin resonance (ESR) and Mössbauer measurements, and theoretically by density functional calculations. The resulting single-crystal structure (a = 15.6991(9) Å; b = 5.3323 (4) Å; c = 10.8875(6) Å; S.G. Pbna) consists of edge-shared SbO6 octahedral chains, which alternate with vertex-linked, magnetically active FeO4 tetrahedral chains. The 57Fe Mössbauer spectra confirmed the presence of high-spin Fe3+ (3d5) ions in a distorted tetrahedral oxygen coordination. The magnetic susceptibility and specific heat data show the absence of a long-range magnetic ordering in Na2FeSbO5 down to 2 K, but ac magnetic susceptibility unambigously demonstrates spin-glass-type behavior with a unique two-step freezing at Tf1 ≈ 80 K and Tf2 ≈ 35 K. Magnetic hyperfine splitting of 57Fe Mössbauer spectra was observed below T* ≈ 104 K (Tf1 < T*). The spectra just below T* (Tf1 < T < T*) exhibit a relaxation behavior caused by critical spin fluctuations, indicating the existence of short-range correlations. The stochastic model of ionic spin relaxation was used to account for the shape of the Mössbauer spectra below the freezing temperature. A complex slow dynamics is further supported by ESR data revealing two different absorption modes presumably related to ordered and disordered segments of spin chains. The data imply a spin-cluster ground state for Na2FeSbO5.

High‐Pressure Phase Transition of Iron: A Combined Magnetic Remanence and Mössbauer Study

AbstractWe measured Mössbauer spectra and the acquisition of saturation isothermal remanent magnetization in alternating steps on the same sample of polycrystalline, multidiron metal powder in a diamond anvil cell across the body centered cubic (bcc) to hexagonal closed packed (hcp) phase transition at room temperature up to 19.2 GPa. Within the bcc stability field indicated by the presence of magnetic hyperfine splitting, saturation remanent magnetization and sextet area were well correlated during compression and decompression. The areas and dips of the outer (first and sixth) and middle (second and fifth) components of the sextet changed in relative proportion as a function of pressure, which was attributed to rotation of the magnetization direction perpendicular to the gamma‐ray source. Sextet peaks disappeared above ∼15 GPa, yet magnetic remanence persisted. Magnetic remanence intensity divided by the fractional area of the sextet, taken to represent bcc Fe, attained maxima at pressures near the boundaries of the hysteretic transition, which we attribute to strain‐related magnetostriction effects associated with a distorted bcc‐hcp phase. Magnetic remanence observed within the hcp stability field, as defined by the absence of sextet peaks, could be due to a previously described, distorted bcc‐hcp phase whose hyperfine field was below detection limits of Mössbauer spectroscopy. Our study suggests that distorted bcc‐hcp Fe holds magnetic remanence and leaves open the possibility that this phase carries magnetic remanence into the pressure range where only pure hcp Fe is considered stable.

Mössbauer spectra of iron (III) sulfide particles

Trivalent iron sulfide (Fe2 S 3) particles were synthesized using a modified polyol method. These particles exhibited a needle-like shape (diameter = 10-50 nm, length = 350-1000 nm) and generated a clear XRD pattern. Mossbauer spectra of the product showed a paramagnetic doublet at room temperature and distributed hyperfine magnetic splitting at low temperature. The Curie temperature of this material was determined to be approximately 60 K. The data suggest that the Fe2 S 3 had a structure similar to that of maghemite (γ-Fe2 O 3) with a lattice constant of a = 10.6 A. The XRD pattern calculated from this structure was in agreement with the experimental pattern and the calculated hyperfine magnetic field was also equivalent to that observed in the experimental Mossbauer spectrum.

Iron state in iron nanoparticles with and without zirconium

Mossbauer and X-ray methods are used for investigations of structure, stability and characteristics of pure-iron grain and two iron-zirconium alloys such as Fe + 5 wt.% Zr and Fe + 10 wt.% Zr. The used powder was ground for 24 h in a SPEX Model 8000 mill shaker. Complex nanoparticles are found, which change their properties under milling. Mossbauer spectral parameters are obtained for investigated materials. Milling results in formation of nanosized particles with two states of iron atoms: one main part is pure α-Fe and another part of iron atoms displaced in grain boundaries or defective zones in which hyperfine magnetic splitting decrease to ∼ 30.0 T. In alloys with Zr three iron states are formed in each alloy, main part of iron is in the form of α-Fe and another two states depend on the concentration of Zr and represent iron in grain boundaries with Zr atoms in nearest neighbor. The changing of iron states is discussed.

Collective radiation spectrum for ensembles with Zeeman splitting in single-photon superradiance

In an ensemble of identical atoms, cooperative effects like sub- or superradiance may alter the decay rates and the energy of specific transitions may be shifted from the single-atom value by the so-called collective Lamb shift. While such effects in ensembles of two-level systems are by now well understood, realistic multi-level systems are more difficult to handle. In this work we show that in a system of atoms or nuclei under the action of an external magnetic field, the collective contribution to the level shifts can amount to seizable deviations from the single-atom Zeeman or magnetic hyperfine splitting picture. We develop a formalism to describe single-photon superradiance in multi-level systems in the small sample limit and quantify the parameter regime for which the collective Lamb shift leads to measurable deviations in the magnetic-field-induced splitting. In particular, we show that this effect should be observable in the nuclear magnetic hyperfine splitting in M\"ossbauer nuclei embedded in thin-film x-ray cavities.

Mixed europium valence in Eu0.937Ba8[BN2]6 – Structure and spectroscopic behavior

Polycrystalline samples of Sr0.95Eu0.05Ba8[BN2]6 and Eu0.937Ba8[BN2]6 were synthesized via conventional solid-state reaction from the binary precursor compounds Sr3N2, EuN, Ba3N2 and BN at 1000 °C. The structure of Eu0.937Ba8[BN2]6 was refined from single crystal X-ray diffractometer data: Eu0.937Ba8[BN2]6 type, Fd3¯m, a = 1594.54(9) pm, wR2 = 0.0654, 380 F2 values and 23 variables. The 8a europium site shows an occupancy of only 93.7(9) % suggesting partial oxidation of europium to fulfil an electron-precise description, i. e. EuII0.81EuIII0.13Ba8[BN2]6. The mixed europium valence was confirmed by magnetic susceptibility measurements (reduced magnetic moment of 7.28 μB per europium atom) and 151Eu Mössbauer spectroscopy (EuII: EuIII = 82: 18). The nitridoborate anions are coordinated by slightly distorted, mono-capped (europium) square prisms formed by the barium atoms. All metal cations are hexa-coordinated by nitrogen atoms. The EPR spectra of EuxSr1-xBa8[BN2]6 samples (0.001 ≤ x ≤ 0.01) suggest close to cubic local symmetry of the Eu2+ dopant ions and reveal some highly unusual features: Magnetic hyperfine splitting is only observed with one of the Eu nuclear isotopes, and the coupling constant of 243.6 MHz is extremely large compared to values (90–100 MHz) typically observed in the literature for Eu2+ doped crystalline materials.

High-Pressure NiAs-Type Modification of FeN.

The combination of laser‐heated diamond anvil cells and synchrotron Mössbauer source spectroscopy were used to investigate high‐temperature high‐pressure chemical reactions of iron and iron nitride Fe2N with nitrogen. At pressures between 10 and 45 GPa, significant magnetic hyperfine splitting indicated compound formation after annealing at 1300 K. Subsequent in situ X‐ray diffraction reveals a new modification of FeN with NiAs‐type crystal structure, as also rationalized by first‐principles total‐energy and chemical‐bonding studies.

Magnetic interactions in NiO at ultrahigh pressure

Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV M\"ossbauer transition of $^{61}\mathrm{Ni}$. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to $\ensuremath{\sim}24$ T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.

Spectroscopic and Theoretical Study of Spin-Dependent Electron Transfer in an Iron(III) Superoxo Complex.

It was shown previously (J. Am. Chem. Soc. 2014, 136, 10846) that bubbling of O2 into a solution of Fe(II)(BDPP) (H2BDPP = 2,6-bis[[(S)-2-(diphenylhydroxymethyl)-1-pyrrolidinyl]methyl]pyridine) in tetrahydrofuran at -80 °C generates a high-spin (SFe = (5)/2) iron(III) superoxo adduct, 1. Mössbauer studies revealed that 1 is an exchange-coupled system, [Formula: see text], where SR = (1)/2 is the spin of the superoxo radical, of which the spectra were not well enough resolved to determine whether the coupling was ferromagnetic (S = 3 ground state) or antiferromagnetic (S = 2). The glass-forming 2-methyltetrahydrofuran solvent yields highly resolved Mössbauer spectra from which the following data have been extracted: (i) the ground state of 1 has S = 3 (J < 0); (ii) |J| > 15 cm(-1); (iii) the zero-field-splitting parameters are D = -1.1 cm(-1) and E/D = 0.02; (iv) the major component of the electric-field-gradient tensor is tilted ≈7° relative to the easy axis of magnetization determined by the MS = ±3 and ±2 doublets. The excited-state MS = ±2 doublet yields a narrow parallel-mode electron paramagnetic resonance signal at g = 8.03, which was used to probe the magnetic hyperfine splitting of (17)O-enriched O2. A theoretical model that considers spin-dependent electron transfer for the cases where the doubly occupied π* orbital of the superoxo ligand is either "in" or "out" of the plane defined by the bent Fe-OO moiety correctly predicts that 1 has an S = 3 ground state, in contrast to the density functional theory calculations for 1, which give a ground state with both the wrong spin and orbital configuration. This failure has been traced to a basis set superposition error in the interactions between the superoxo moiety and the adjacent five-membered rings of the BDPP ligand and signals a fundamental problem in the quantum chemistry of O2 activation.

Mössbauer spectroscopic studies of Al3+ ions substitution effects in superparamagnetic Mg0.2Mn0.5Ni0.3AlyFe2−yO4 compositions

Nanoparticles of Al3+ ions substituted MgMnNi materials with compositions Mg0.2Mn0.5Ni0.3AlyFe2−yO4 (y = 0.15–0.25) were synthesized by citrate precursor technique. Samples were characterized by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and room temperature 57Fe Mössbauer spectroscopy. Saturation magnetization decreases with increasing Al3+ ions concentration because replacement of Fe3+ ions by Al3+ ions at octahedral B-site weaken sublattice interaction and lowers magnetic moments. Mössbauer spectral studies show that as-prepared nano-sized samples are superparamagnetic at room temperature. Superparamagnetic relaxation was observed for small crystallite in samples with higher Al content, which is attributed to weakening of A–B exchange interaction. Mössbauer spectra at 300 K show a gradual collapse of magnetic hyperfine splitting typical for superparamagnetic relaxation. An increase in inversion parameter is observed with increasing Al3+ ions substitution, which is attributed to decrease in crystallite size.

Mössbauer spectroscopy, magnetization, magnetic susceptibility, and low temperature heat capacity of α-Na2NpO4

The physical and chemical properties at low temperatures of hexavalent disodium neptunate α-Na2NpO4 are investigated for the first time in this work using Mössbauer spectroscopy, magnetization, magnetic susceptibility, and heat capacity measurements. The Np(VI) valence state is confirmed by the isomer shift value of the Mössbauer spectra, and the local structural environment around the neptunium cation is related to the fitted quadrupole coupling constant and asymmetry parameters. Moreover, magnetic hyperfine splitting is reported below 12.5 K, which could indicate magnetic ordering at this temperature. This interpretation is further substantiated by the existence of a λ-peak at 12.5 K in the heat capacity curve, which is shifted to lower temperatures with the application of a magnetic field, suggesting antiferromagnetic ordering. However, the absence of any anomaly in the magnetization and magnetic susceptibility data shows that the observed transition is more intricate. In addition, the heat capacity measurements suggest the existence of a Schottky-type anomaly above 15 K associated with a low-lying electronic doublet found about 60 cm−1 above the ground state doublet. The possibility of a quadrupolar transition associated with a ground state pseudoquartet is thereafter discussed. The present results finally bring new insights into the complex magnetic and electronic peculiarities of α-Na2NpO4.