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Methanotrophic bacteria utilize the nonheme diiron enzyme soluble methane monooxygenase (sMMO) to convert methane to methanol in the first step of their metabolic cycle under copper-limiting conditions. The structure of the sMMO Fe(IV)2 intermediate Q responsible for activating the inert C-H bond of methane (BDE = 104 kcal/mol) remains controversial, with recent studies suggesting both "open" and "closed" core geometries for its active site. In this study, we employ nuclear resonance vibrational spectroscopy (NRVS) to probe the geometric and electronic structure of intermediate Q at cryogenic temperatures. These data demonstrate that Q decays rapidly during the NRVS experiment. Combining data from several years of measurements, we derive the NRVS vibrational features of intermediate Q as well as its cryoreduced decay product. A library of 90 open and closed core models of intermediate Q is generated using density functional theory to analyze the NRVS data of Q and its cryoreduced product as well as prior spectroscopic data on Q. Our analysis reveals that a subset of closed core models reproduce these newly acquired NRVS data as well as prior data. The reaction coordinate with methane is also evaluated using both closed and open core models of Q. These studies show that the potent reactivity of Q toward methane resides in the "spectator oxo" of its Fe(IV)2O2 core, in contrast to nonheme mononuclear Fe(IV)═O enzyme intermediates that H atoms abstract from weaker C-H bonds.

Methanotrophic bacteria utilize the non-heme diiron enzyme soluble methane monooxygenase (sMMO) to convert methane to methanol in the first step of their metabolic cycle under copper-limiting conditions. The structure of the sMMO Fe(IV)(2) intermediate Q responsible for activating the inert C-H bond of methane (BDE = 104 kcal/mol) remains controversial, with recent studies suggesting both “open” and “closed” core geometries for its active site. In this study, we employ nuclear resonance vibrational spectroscopy (NRVS) to probe the geometric and electronic structure of intermediate Q at cryogenic temperatures. These data demonstrate that Q decays rapidly during the NRVS experiment. Combining data from several years of measurements, we derive the NRVS vibrational features of intermediate Q as well as its cryoreduced decay product. A library of 90 open and closed core models of intermediate Q is generated using density functional theory (DFT) to analyze the NRVS data of Q and its cryoreduced product, as well as prior spectroscopic data on Q. Our analysis reveals that a subset of closed core models reproduce these newly acquired NRVS data as well as prior data. The reaction coordinate with methane is also evaluated using both closed and open core models of Q. These studies show that the potent reactivity of Q towards methane resides in the “spectator oxo” of its Fe(IV)(2)O(2) core, in contrast to non-heme mononuclear Fe(IV)=O enzyme intermediates that H-atom abstract from weaker C-H bonds.

The pterin-dependent nonheme iron enzymes hydroxylate aromatic amino acids to perform the biosynthesis of neurotransmitters to maintain proper brain function. These enzymes activate oxygen using a pterin cofactor and an aromatic amino acid substrate bound to the Fe(II) active site to form a highly reactive Fe(IV) = O species that initiates substrate oxidation. In this study, using tryptophan hydroxylase, we have kinetically generated a pre-Fe(IV) = O intermediate and characterized its structure as a Fe(II)-peroxy-pterin species using absorption, Mössbauer, resonance Raman, and nuclear resonance vibrational spectroscopies. From parallel characterization of the pterin cofactor and tryptophan substrate–bound ternary Fe(II) active site before the O(2) reaction (including magnetic circular dichroism spectroscopy), these studies both experimentally define the mechanism of Fe(IV) = O formation and demonstrate that the carbonyl functional group on the pterin is directly coordinated to the Fe(II) site in both the ternary complex and the peroxo intermediate. Reaction coordinate calculations predict a 14 kcal/mol reduction in the oxygen activation barrier due to the direct binding of the pterin carbonyl to the Fe(II) site, as this interaction provides an orbital pathway for efficient electron transfer from the pterin cofactor to the iron center. This direct coordination of the pterin cofactor enables the biological function of the pterin-dependent hydroxylases and demonstrates a unified mechanism for oxygen activation by the cofactor-dependent nonheme iron enzymes.

This paper presents an absolute X-ray photon energy measurement method that uses a Bond diffractometer. The proposed system enables the prompt and rapid in situ measurement of photon energies over a wide energy range. The diffractometer uses a reference silicon single-crystal plate and a highly accurate angle encoder called SelfA. The performance of the system is evaluated by repeatedly measuring the energy of the first excited state of the potassium-40 nuclide. The excitation energy is determined as 29829.39 (6) eV, and this is one order of magnitude more accurate than the previous measurement. The estimated uncertainty of the photon energy measurement was 0.7 p.p.m. as a standard deviation and the maximum observed deviation was 2 p.p.m.

In order to clarify the spin order of FeV2O4, 57Fe Mossbauer spectroscopy has been conducted by using a single crystal specimen. A measurement in applied magnetic field has been also conducted. By applying a slight compression in the sample plane, almost single domain state was achieved in the low temperature phases. The spectra consist of Fe2+ spectra (~ 85%) and Fe2.5+ spectra (~ 15%), corresponding to the A- and B-site Fe ions, respectively. The B-site spectrum well represents the local structure and the magnetic structure of V3+ ion on the B-site. Notable changes in the Mossbauer parameters are recognized at 140, 110, and 65 K, where the successive phase transitions take place. The feature well represents the orbital and spin order. In the orthorhombic phase below 110 K, Fe2+ and V3+ spins form a collinear ferrimagnetic order along the a-axis. Below 65 K in the low temperature tetragonal phase, however, both spins incline from the c-axis to form a canted ferrimagnetic structure. The canting angles are about 17° and 52° at 4.2 K for Fe2+ and V3+ spins, respectively.

We investigated the magnetic properties of multiferroic hexagonal ErFeO3 thin films by using x-ray magnetic circular dichroism (XMCD) and synchrotron Mössbauer spectroscopy. In order to reveal the element-specific magnetic properties, temperature-dependent XMCD experiments were conducted at the Fe L 2,3 and Er M 4,5-edges. Apparent magnetic hysteresis loops appear for both ions below the Néel temperature, which suggests the existence of ferromagnetism. The temperature evolutions of the coercive field and spontaneous magnetization for both ions show similar behavior. These results indicate that Fe ions influence the magnetism of Er ions. Our results deepen the understanding of the physical properties of hexagonal rare-earth ferrite system.

Binuclear non-heme iron enzymes activate O2 for diverse chemistries that include oxygenation of organic substrates and hydrogen atom abstraction. This process often involves the formation of peroxo-bridged biferric intermediates, only some of which can perform electrophilic reactions. To elucidate the geometric and electronic structural requirements to activate peroxo reactivity, the active peroxo intermediate in 4-aminobenzoate N-oxygenase (AurF) has been characterized spectroscopically and computationally. A magnetic circular dichroism study of reduced AurF shows that its electronic and geometric structures are poised to react rapidly with O2. Nuclear resonance vibrational spectroscopic definition of the peroxo intermediate formed in this reaction shows that the active intermediate has a protonated peroxo bridge. Density functional theory computations on the structure established here show that the protonation activates peroxide for electrophilic/single-electron-transfer reactivity. This activation of peroxide by protonation is likely also relevant to the reactive peroxo intermediates in other binuclear non-heme iron enzymes.

We report the temperature variation of the $^{119}\mathrm{Sn}$-M\"ossbauer spectra of the antiperovskite (inverse perovskite) oxide superconductor ${\mathrm{Sr}}_{3\ensuremath{-}x}\mathrm{SnO}$. Both superconductive (Sr deficient) and nonsuperconductive (nearly stoichiometric) samples exhibit major $\ensuremath{\gamma}$-ray absorption with an isomer shift similar to that of ${\mathrm{Mg}}_{2}\mathrm{Sn}$. This fact shows that ${\mathrm{Sr}}_{3\ensuremath{-}x}\mathrm{SnO}$ contains the metallic anion ${\mathrm{Sn}}^{4\ensuremath{-}}$, which is rare, especially among oxides. In both samples, we observed another $\ensuremath{\gamma}$-ray absorption with a larger isomer shift, indicating that there is another ionic state of Sn with a higher oxidation number. The temperature dependence of the absorption intensities reveals that the Sn ions exhibiting larger isomer shifts have a lower energy of the local vibration. The larger isomer shift and lower vibration energy are consistent with the values estimated from the first-principles calculations for hypothetical structures with various Sr-deficiency arrangements. Therefore, we conclude that the additional $\ensuremath{\gamma}$-ray absorptions originate from the Sn atoms neighboring the Sr deficiency.

We successfully observed the synchrotron-radiation-based Mossbauer absorption spectra with 158Gd and 99Ru. Their nuclear resonant energies were 79.5 keV and 89.6 keV, respectively, and they are factually the highest energy which energy region synchrotron radiation covers with sufficient intensity as the incident X-rays for Mossbauer spectroscopy. Although the low recoilless fraction owing to these high resonant energy, Mossbauer energy spectra of GdPd3 to 158Gd2O3 and fcc-Ru nanoparticles to bulk hcp-99Ru metal were obtained with natural samples of the former compounds with sufficient amount, because of the high transparency of these high energy X-rays(to electronic scattering). In spite of large statistical errors, we can evaluate the hyperfine parameters when the spectrum includes simple 1-site profile. 99Ru and 158Gd SR-based Mossbauer absorption spectra of various complex materials including somewhat complex structures will be available with the improvements to the measurement system; More detector elements for larger solid angle subtended to the scatterer sample will yields more counting rates and improvement higher recoilless fraction by arranging more appropriate chemical specimen as the scatterer yields deeper absorption profile.

A parent compound of iron-based superconductor, Fe1.1Te, and a Se-doped superconductor, FeTe0.5Se0.5, were investigated using 125Te-Mossbauer spectroscopy. By measuring precise temperature dependence of the spectra, discontinuous line broadening in the Fe1.1Te near the antiferromagnetic transition temperature (TN) of Fe was observed. While the broadening of the line width were observed in both samples as the temperature decreases, the temperature dependences of the line width were well reproduced as that of the recoilless fraction, assuming the Debye model with a Debye temperature of about 200 K. The discontinuous additional line broadening in the Fe1.1Te can be considered as the internal magnetic fields of Te below TN, since the temperature dependence of internal magnetic fields of Te is similar to that of Fe in 57Fe-Mossbauer spectroscopy. Therefore, hybridization of the electronic orbital of Te and Fe was suggested and the transferred magnetic moment of Te was induced through the antiferromagnetic order of Fe at TN.

Due to technical constraints this article was published in volume 240:1 with erroneous article citation ID number 5 whereas this should have been 75 which is corrected as such. Springer Nature sincerely apologizes towards the author(s) for the inconvenience caused.

We have newly developed 166Er Mossbauer spectroscopy in Institute for Integrated Radiation and Nuclear Science, Kyoto University (KURNS). As 166Ho radioactive source, HoAl2 was used. The compound was irradiated in the nuclear reactor (1 MW) for 5 min. The source has the intensity of 19 MBq and the half-life of 26.8 h. It is our privilege to conduct measurement immediately after the preparation of the radioactive source, since the spectroscopic equipment is situated just next to the reactor. The spectra of three typical Er oxides, Er2O3, ErFeO3, and ErMnO3 were measured at 40 K. On the basis of the calculated asymmetry parameter η and the evaluated sign of the quadrupole coupling constant e2qQ/2 from the structure parameters, we have successfully analyzed the spectra by using the quadrupole Hamiltonian assuming the transmission integral line shapes. The 166Er Mossbauer parameters, isomer shift IS, e2qQ/2, and line width W were obtained for the three specimens.

Bulk superconductivity was recently reported in the antiperovskite oxide Sr3−xSnO, with a possibility of hosting topological superconductivity. We investigated the evolution of superconducting properties such as the transition temperature Tc and the size of the diamagnetic signal, as well as normal-state electronic and crystalline properties, with varying the nominal Sr deficiency x0. Polycrystalline Sr3−xSnO was obtained up to x0 = 0:6 with a small amount of SrO impurities. The amount of impurities increases for x0 > 0.6, suggesting phase instability for high deficiency. Mössbauer spectroscopy reveals an unusual Sn4− ionic state in both stoichiometric and deficient samples. By objectively analyzing superconducting diamagnetism data obtained from a large number of samples, we conclude that the optimal x0 lies in the range 0.5 x0 3−xSnO but with varying intensities. These results clarify the Sr deficiency dependence of the normal and superconducting properties of the antiperovskite oxide Sr3−xSnO will ignite future work on this class of materials.

The measurement of the nuclear resonant small-angle scattering was achieved by scanning the position of a multi-element avalanche photodiode detector, detecting delayed nuclear resonant signal to investigate microstructures of the electronic states. The nuclear resonant small-angle scattering has been attempted to study the coexisting phase of superconductivity and magnetic order in an under-doped Fe-based superconductor, Ba0.8K0.2Fe2As2. Clear change was not observed in the exponent of the angular profile of the nuclear resonant small-angle scattering in the coexisting temperature. This fact implies the microstructure in the coexisting phase does not have an obvious typical scale but a complex spatial texture. Another attempt was performed for the microstructure in the magnetic properties in an anti-invar fcc Fe-Ni-C alloy to investigate mechanism of the anti-invar properties. An enhancement of the angular profile in a few tens of nm range was observed as decreasing the temperature down to a little below the Curie temperature. This fact implies the existence of the inhomogeneity of magnetically-ordered phase in this range of size, which may related to the anti-invar properties.

Thorium-229 is a unique case in nuclear physics: it presents a metastable first excited state Th-229m, just a few electronvolts above the nuclear ground state. This so-called isomer is accessible by VUV lasers, which allows transferring the amazing precision of atomic laser spectroscopy to nuclear physics. Being able to manipulate the Th-229 nuclear states at will opens up a multitude of prospects, from studies of the fundamental interactions in physics to applications as a compact and robust nuclear clock. However, direct optical excitation of the isomer or its radiative decay back to the ground state has not yet been observed, and a series of key nuclear structure parameters such as the exact energies and half-lives of the low-lying nuclear levels of Th-229 are yet unknown. Here we present the first active optical pumping into Th-229m. Our scheme employs narrow-band 29 keV synchrotron radiation to resonantly excite the second excited state, which then predominantly decays into the isomer. We determine the resonance energy with 0.07 eV accuracy, measure a half-life of 82.2 ps, an excitation linewidth of 1.70 neV, and extract the branching ratio of the second excited state into the ground and isomeric state respectively. These measurements allow us to re-evaluate gamma spectroscopy data that have been collected over 40~years.

We developed a measurement system that enables the reconstruction of {\gamma}-ray time spectra in cascade decay schemes. As this system records all the time and energy information of {\gamma}-rays, reconstruction is possible after the measurement. Therefore, the energy regions for the {\gamma}-ray identification can be optimized in complicated cascade decay schemes. Moreover, in this system we can record data with time-dependent parameters of external perturbations, such as applied magnetic fields, and consequently we can investigate the correlations and responses of {\gamma}-rays to the perturbation. This property fulfills the demands required for quantum information research with {\gamma}-rays., Comment: 7 pages with 3 figures

We have studied 151Eu Mossbauer effects on EuRh2Si2 at a high pressure of 1.0 GPa as well as at ambient pressure. The compound shows a temperature-induced valence transition from the Eu2+ state to ...

We elucidate the magnetic phases and superconducting (SC) transition temperatures (T

Bulk superconductivity was recently reported in the antiperovskite oxide Sr3−xSnO, with a possibility of hosting topological superconductivity. We investigated the evolution of superconducting properties such as the transition temperature Tc and the size of the diamagnetic signal, as well as normal-state electronic and crystalline properties, with varying the nominal Sr deficiency x0. Polycrystalline Sr3−xSnO was obtained up to x0 = 0:6 with a small amount of SrO impurities. The amount of impurities increases for x0 > 0.6, suggesting phase instability for high deficiency. Mössbauer spectroscopy reveals an unusual Sn4− ionic state in both stoichiometric and deficient samples. By objectively analyzing superconducting diamagnetism data obtained from a large number of samples, we conclude that the optimal x0 lies in the range 0.5

The Rieske dioxygenases are a major subclass of mononuclear nonheme iron enzymes that play an important role in bioremediation. Recently, a high-spin FeIII–(hydro)-peroxy intermediate (BZDOp) has been trapped in the peroxide shunt reaction of benzoate 1,2-dioxygenase. Defining the structure of this intermediate is essential to understanding the reactivity of these enzymes. Nuclear resonance vibrational spectroscopy (NRVS) is a recently developed synchrotron technique that is ideal for obtaining vibrational, and thus structural, information on Fe sites, as it gives complete information on all vibrational normal modes containing Fe displacement. In this study, we present NRVS data on BZDOp and assign its structure using these data coupled to experimentally calibrated density functional theory calculations. From this NRVS structure, we define the mechanism for the peroxide shunt reaction. The relevance of the peroxide shunt to the native FeII/O2 reaction is evaluated. For the native FeII/O2 reaction, an FeIII–superoxo intermediate is found to react directly with substrate. This process, while uphill thermodynamically, is found to be driven by the highly favorable thermodynamics of proton-coupled electron transfer with an electron provided by the Rieske [2Fe-2S] center at a later step in the reaction. These results offer important insight into the relative reactivities of FeIII–superoxo and FeIII–hydroperoxo species in nonheme Fe biochemistry.

We elucidate the magnetic phases and superconducting transition temperatures (Tc) in Sr2VFeAsO3-delta (21113V), an iron-based superconductor with a thick-blocking layer fabricated from a perovskite-related transition metal oxide. At low temperatures (T < 37.1 K), 21113V exhibited a superconducting phase in the range 0.031 =< delta =< 0.145 and an antiferromagnetic (AFM) iron sublattice in the range 0.267 =< delta =< 0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031 =< delta =< 0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124 =< delta =< 0.664. The Ferri. phase was the most dominant at a delta value of 0.267, showing an AFM phase of Fe at T < 20 K. Increasing the spontaneous magnetic moments reduced the magnetic shielding volume fraction due to the superconducting phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The Tc-delta curve showed two maxima. The smaller and larger of Tc maxima occurred at delta = 0.073 and delta = 0.145, respectively; the latter resides on the phase boundary between AFM and the partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new mechanisms of Tc enhancement in iron-based superconductors., 34 pages, 10 figures, 2 tables, supplement information with 11 pages, 8 figures, 3 tables. accepted for publication, J. Phys.: Condens. Matter, Updated manuscript contains More references and readability. See http://iopscience.iop.org/article/10.1088/1361-648X/aaf7e0

We obtained energy-domain 61Ni synchrotron-radiation-based Mossbauer absorption spectra of three materials that relate to nanoparticles: Ni2(C8O6H2) metal-organic frameworks (MOFs), Ni nanoparticles synthesized by complete heat decomposition of the MOFs, and the composites of Ni nanoparticles and the MOFs synthesized by partial decomposition of the MOFs. The 61Ni abundance of all the samples was not enriched but we were successfully able to obtain their spectra in 1 day or less, by using a highly efficient measurement system where the internal conversion electrons from energy standard 61Ni86V14 foil were detected. Although both nanoparticle constituent and MOF constituent in the composites included Ni atoms, the Mossbauer parameters of the Ni nanoparticle constituent could be evaluated; the magnetic hyperfine field of the Ni nanoparticle constituent in the composites was different from that of the Ni nanoparticles obtained by the complete heat decomposition. This difference implied that the 3d and/or 4s electron configuration of the nanoparticle constituent were affected by the MOF constituent in the composites.

Synchrotron-radiation-based Mossbauer spectroscopy that yields absorption type Mossbauer spectra has been applied to various isotopes. This method enables the advanced measurement by using the excellent features of synchrotron radiation, such as Mossbauer spectroscopic measurement under high-pressures. Furthermore, energy selectivity of synchrotron radiation allows us to measure 40K Mossbauer spectra, of which observation is impossible by using ordinary radioactive sources because the first excited state of 40K is not populated by any radioactive parent nuclides. Moreover, this method has flexibility of the experimental setup that the measured sample can be used as a transmitter or a scatterer, depending on the sample conditions. To enhance the measurement efficiency of the spectroscopy, we developed a detection system in which a windowless avalanche photodiode (APD) detector is combined with a vacuum cryostat to detect internal conversion electrons adding to X-rays accompanied by nuclear de-excitation. In particular, by selecting the emission from the scatterer sample, depth selective synchrotron-radiation-based Mossbauer spectroscopy is possible. Furthermore, limitation of the time window in the delayed components enables us to obtain narrow linewidth in Mossbauer spectra. Measurement system that records velocity dependent time spectra and energy information simultaneously realizes the depth selective and narrow linewidth measurement.

The Mossbauer spectra of the 35.49 keV excited state of 125Te were observed in the energy domain using synchrotron radiation for the first time. The obtained isomer shifts and Debye temperature agree with previous experiments. These results show that this method will be applicable to various compounds.

Characteristic relaxation times τ of the microscopic correlation in o-terphenyl and glycerol were obtained by a time-domain interferometry method using nuclear resonant scattering of synchrotron radiation. From the temperature dependence of τ, a new decoupling temperature 278 K, which is below the conventional decoupling temperature 290 K, was obtained for o-terphenyl. Furthermore, we found a liquid-like relation between τ and q (momentum transfer) as $\tau \propto q^{-2}$ at 285 K in o-terphenyl and 260 and 265 K in glycerol. However, an anomalous q dependence of the slow β relaxation time, $\tau \propto q^{-2.9}$ and q −3.8, was observed in deeply supercooled (265 K) and glass (240 K) states, respectively, in o-terphenyl, indicating specially restricted dynamics of the slow β process.

(129)I Mössbauer spectroscopy was applied to water-vapor-responsive MMX-type quasi-one-dimensional iodide-bridged Pt complexes (MMX chains) in order to investigate their electronic state quantitatively. Two sets of octuplets observed in K2(H3NC3H6NH3)[Pt2(pop)4I]·4H2O (2·4H2O) and one octuplet observed in K2(cis-H3NCH2CH=CHCH2NH3)[Pt2(pop)4I]·4H2O (1·4H2O) and dehydrated complexes (1 and 2) indicate a unique alternating charge-polarization + charge-density-wave (ACP + CDW) electronic state and a charge-density-wave (CDW) electronic state, respectively. These spectra correspond to their crystal structure and the change of electronic states upon dehydration. Since these complexes consist of an alternating array of positively charged and negatively charged layers, the charge on the iodide ion (ρIS) was discussed on the basis of the isomer shift (IS). The ρIS of the water-vapor-responsive MMX chains was mainly -0.13 to -0.21, which are the smallest of all MMX chains reported so far. Hence, it indicates that the negative charge on the iodide ion is strongly donated to the Pt ion in these complexes. This covalent interaction predominates in the ACP + CDW state as well as in the CDW state. Therefore, the ACP + CDW state is in fact the CDW state with the ACP-type lattice distortion. Because the ρIS became smaller with the decreasing Pt-I-Pt distance, it can be concluded that the covalent interaction plays an important role in determining the electronic states of the MMX chains with pop (= P2H2O5(2-)) ligands.

A Mossbauer spectroscopy study of the iron-based superconductor KxFe2−ySe2, with two superconducting phases of SC1 and a pressure induced SC2 was performed under pressure. This compound consists of...

Introduction Although α-Fe2O3 is promising anode material of LIB for excellent theoretical capacity as 1007 mAhg-1, it shows the severe cycle deterioration due to conversion reaction during the charge-discharge process. We have considered that the formation of Fe2O3-Al2O3 solid solution allows the Fe ions to react reversibly around the original site in the corundum-type structure. Although both α-Fe2O3 and α-Al2O3 have the corundum-type structure, solid solution ranges are restricted within 10% from the both end components [1]. In recent years, we have successfully obtained the Fe2O3-Al2O3 solid solution for all the compositional range through the mechanochemical synthesis method. It was also found that the obtained solid solution shows good cycle characteristics as an anode material of LIB [2]. Nevertheless, this solid solution has just been newly found and any magnetic property has not been clarified yet. In this study, we have carried out the Mössbauer measurement to discuss the magnetic properties of Fe2O3-Al2O3 solid solution. Experimental The solid solutions of (Fe2O3)1-x(Al2O3)x (x = 0, 0.1, 0.25, 0.33, 0.50 and 0.67) were prepared by mechanical alloying method. About 0.5 g of the stoichiometric mixtures of γ-Fe2O3 and γ-Al2O3 were put into a silicon nitride milling vessel with 20 ml in volume accompanied by 10 silicon nitride balls with 10 mm in diameter without any solvent. A planetary ball milling machine has been operated with the rotation speed of 800 rpm for 240 min. Mössbauer measurement was performed on the obtained samples of (Fe1-xAlx)2O3 (x = 0, 0.1, 0.25, 0.33 ,0.50 and 0.67) at room temperature. 57Co was used as a gamma ray source for Mössbauer measurement. Results and Discussions Fig. 1 shows the Mössbauer spectra of (Fe1-xAlx)2O3 measured at room temperature for x = 0, 0.1, 0.25, 0.33, 0.5 and 0.67. For the Fe2O3 (x = 0) obtained by milling, the sextet spectrum was observed. This would correspond to weak ferromagnetism appearing from a cant structure, in which the spin of Fe is slightly inclined from 90° to the c-axis direction. This spectrum is essentially similar to the α-Fe2O3 reagent without milling. The Mössbauer spectra gradually changed into doublet with increasing the concentration of aluminum x and the change is almost completed to the x = 0.5. Fourier transform of the EXAFS signal shows that |χ| peak value around 1.5 Å corresponding to Fe-O distance did not vary significantly, while that around 2.5 Å for Fe-Fe distance decrease with x. Dilution of Fe3+ with Al3+ would result in the change in spin interaction, or (Fe1-xAlx)2O3 changes from weak ferromagnetism to the paramagnetic state by reducing spin interaction. References [1] A. Muan, C.L. Gee, J. Am. Ceram. Soc., 39 207-214 (1956). [2] S. Takai, E. Sawada, J. Harada, S. Park, M. Oda, S. Esaki, M. Nishijima, T. Yoshie, T. Yabutsuka, T. Yao, Solid State Ionics, 313 1-6 (2017). Figure 1

Mononuclear non-haem iron (NHFe) enzymes catalyse a broad range of oxidative reactions, including halogenation, hydroxylation, ring closure, desaturation and aromatic ring cleavage reactions. They are involved in a number of biological processes, including phenylalanine metabolism, the production of neurotransmitters, the hypoxic response and the biosynthesis of secondary metabolites. The reactive intermediate in the catalytic cycles of these enzymes is a high-spin S = 2 Fe(IV)=O species, which has been trapped for a number of NHFe enzymes, including the halogenase SyrB2 (syringomycin biosynthesis enzyme 2). Computational studies aimed at understanding the reactivity of this Fe(IV)=O intermediate are limited in applicability owing to the paucity of experimental knowledge about its geometric and electronic structure. Synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) is a sensitive and effective method that defines the dependence of the vibrational modes involving Fe on the nature of the Fe(IV)=O active site. Here we present NRVS structural characterization of the reactive Fe(IV)=O intermediate of a NHFe enzyme, namely the halogenase SyrB2 from the bacterium Pseudomonas syringae pv. syringae. This intermediate reacts via an initial hydrogen-atom abstraction step, performing subsequent halogenation of the native substrate or hydroxylation of non-native substrates. A correlation of the experimental NRVS data to electronic structure calculations indicates that the substrate directs the orientation of the Fe(IV)=O intermediate, presenting specific frontier molecular orbitals that can activate either selective halogenation or hydroxylation.

We measured the synchrotron-radiation (SR)-based Mössbauer spectra of Ni-based nanoparticles with a hexagonal structure that were synthesised by chemical reduction. To obtain Mössbauer spectra of the nanoparticles without (61)Ni enrichment, we developed a measurement system for (61)Ni SR-based Mössbauer absorption spectroscopy without X-ray windows between the (61)Ni84V16 standard energy alloy and detector. The counting rate of the (61)Ni nuclear resonant scattering in the system was enhanced by the detection of internal conversion electrons and the close proximity between the energy standard and the detector. The spectrum measured at 4 K revealed the internal magnetic field of the nanoparticles was 3.4 ± 0.9 T, corresponding to a Ni atomic magnetic moment of 0.3 Bohr magneton. This differs from the value of Ni3C and the theoretically predicted value of hexagonal-close-packed (hcp)-Ni and suggested the nanoparticle possessed intermediate carbon content between hcp-Ni and Ni3C of approximately 10 atomic % of Ni. The improved (61)Ni Mössbauer absorption measurement system is also applicable to various Ni materials without (61)Ni enrichment, such as Ni hydride nanoparticles.

Synchrotron-radiation (SR) based Mossbauer absorption spectroscopy of various nuclides is reviewed. The details of the measuring system and analysis method are described. Especially, the following two advantages of the current system are described: the detection of internal conversion electrons and the close distance between the energy standard scatterer and the detector. Both of these advantages yield the enhancement of the counting rate and reduction of the measuring time. Furthermore, SR-based Mossbauer absorption spectroscopy of 40K, 151Eu, and 174Yb is introduced to show the wide applicability of this method. In addition to these three nuclides, SR-based Mossbauer absorption spectroscopy of 61Ni, 73Ge, 119Sn, 125Te, 127I, 149Sm, and 189Os has been performed. We continue to develop the method to increase available nuclides and to increase its ease of use. The complementary relation between the time-domain method using SR, such as nuclear forward scattering and the energy-domain methods such as SR-based Mossbauer absorption spectroscopy is also noted.

The slow dynamics of microscopic density correlations in supercooled glycerol was studied by time-domain interferometry using 57Fe-nuclear resonant scattering gamma rays of synchrotron radiation. The dependence of the relaxation time at 250 K on the momentum transfer q is maximum near the first peak of the static structure factor S(q) at q ∼ 15 nm −1. The q-dependent behavior of the relaxation time known as de Gennes narrowing was confirmed in glycerol. Conversely, de Gennes narrowing around the second and third peaks of S(q) at q ∼ 26 nm −1 and 54 nm −1 was not detected. The q dependence of the relaxation time was found to follow a power-law equation with power-law index of 1.9(2) in the q region well above the first peak of S(q) up to ∼ 60 nm −1, which corresponds to angstrom scale, within experimental error. This suggests that in the angstrom-scale dynamics of supercooled glycerol, independent motions dominate over collective motion.

We measured the synchrotron-radiation (SR)-based Mössbauer spectra of Ni-based nanoparticles with a hexagonal structure that were synthesised by chemical reduction. To obtain Mössbauer spectra of the nanoparticles without (61)Ni enrichment, we developed a measurement system for (61)Ni SR-based Mössbauer absorption spectroscopy without X-ray windows between the (61)Ni84V16 standard energy alloy and detector. The counting rate of the (61)Ni nuclear resonant scattering in the system was enhanced by the detection of internal conversion electrons and the close proximity between the energy standard and the detector. The spectrum measured at 4 K revealed the internal magnetic field of the nanoparticles was 3.4 ± 0.9 T, corresponding to a Ni atomic magnetic moment of 0.3 Bohr magneton. This differs from the value of Ni3C and the theoretically predicted value of hexagonal-close-packed (hcp)-Ni and suggested the nanoparticle possessed intermediate carbon content between hcp-Ni and Ni3C of approximately 10 atomic % of Ni. The improved (61)Ni Mössbauer absorption measurement system is also applicable to various Ni materials without (61)Ni enrichment, such as Ni hydride nanoparticles., ニッケルナノ粒子の放射光メスバウアー吸収分光測定に成功 --先端ナノ材料の機能発現メカニズムの解明に期待--. 京都大学プレスリリース. 2016-02-18.

Applications of synchrotron-radiation-based Mossbauer spectroscopy in the “energy domain” to the studies on magnetism of thin films are introduced on the basis of the experiments recently performed at SPring-8, Japan. The measured samples are spintronics-related thin films, such as Co2MnSn films, layered Fe/Cr films, layered Fe/Fe3O4 films, and Fe4N films. The validity of the energy domain measurements is demonstrated in the light of industrial applications of magnetic thin films.

Three porous coordination polymers {Fe(dpa)[Pt(CN)4]·G·nH2O} (1-G; dpa = 1,2-di(4-pyridyl)ethane, G = dpa, bibenzyl (bbz) and stilbene (stb)) have been prepared by using a long and flexible ligand dpa. These compounds formed analogous 3-D elongated Hofmann-type frameworks based on 2-D planar layers extended by Pt–CN–Fe linkages with dpa as flexible pillar ligands. 1-dpa showed a characteristic three-step spin transition (ST) in the temperature range 180–240 K. The ST behavior was reversibly modulated by dehydration and hydration processes in keeping with the three steps. 1-bbz and 1-stb exhibited a gradual three-step ST over the range 80–200 K and an abrupt ST with Tc = 163 K. The guest-dependent cooperativity of the ST behavior is discussed by considering the flexibility of the framework and guest molecules.

The microscopic slow dynamics in various samples has been studied by a time-domain interferometry (TDI) method using nuclear resonant scattering (NRS) of synchrotron radiation and an improvement of the efficiency of TDI is highly desired. To realize it, we developed the TDI method using α-Fe foils with multi-line Mossbauer spectra as nuclear absorbers. Compared to the conventional TDI method using single-line Mossbauer absorbers, the reduction of the measuring time is expected by a simulation study. The simulation study shows a comparatively large change on the multi-line TDI time spectra by the diffusion in a sample and indicates much improvement of the efficiency. We obtained time spectra of the multi-line TDI and the obtained quasi-elastic broadening values of NRS energy width obtained by fitting the time spectra were confirmed to be close to the values obtained by the conventional TDI and estimated standard deviations by the multi-line TDI were comparatively small as expected by the simulation study.

This study reports results of 57Fe Mossbauer spectroscopy and nuclear resonant inelastic scattering (NRIS) in Fe1.1Te. The Fe-specific partial phonon densities of states (PDOSs) were extracted from the observed spectra. No detectable change at the tetragonal-monoclinic phase transition around 65 K was observed. Therefore the variations in lattice constants and/or distortion in FeTe4 tetrahedron through the structural transition was minute. From the observed Fe-PDOS, the Lamb-Mossbauer factor was 0.90(3) at 10 K and the Debye temperature was evaluated as 300(10) K. In 57Fe Mossbauer spectroscopy, the clear magnetic spittings of spectra were measured below Neel temperature. The obtained values of isomer shifts showed characteristics of Fe2+ species and clear difference with the phase transition was observed in temperature dependence of quadrupole splitting (QS). The change of QS must be caused by substantial change of the charge density distribution around the Fe site. This suggests that the band structure or the nature of the Fe-Te bonds becomes highly anisotropic. These results might provide additional information about the respective mechanisms for FeTe1−xSex superconductivity.

Co 2 TiSn Heusler alloy films were grown on MgO substrates at the substrate temperature between 200 and 600 °C using atomically controlled alternate deposition and magnetic hyperfine field at the Sn nuclei was measured by the Mossbauer spectroscopy and the nuclear resonant scattering method. The relation between the hyperfine field and the structural disorder estimated by X-ray diffraction measurements was also examined. The results showed that the sample prepared at higher substrate temperature has higher degree of L2 1 order and larger hyperfine field. For the Co 2 TiSn film grown at 600 °C, the hyperfine field estimated from the oscillatory pattern of the nuclear resonant time spectra was 6.1 T at room temperature and increased with a decrease of temperature to 7.5, 8.1, and 8.3 T at 200, 100, and 5 K, respectively, which shows that the film prepared by this method and condition has almost the same magnetization value and Curie temperature as bulk samples.

One-dimensional iodide-bridged mixed-valence binuclear platinum complexes (the so-called "MMX chains") and their Pt(III) dimer precursors were investigated with (129)I Mossbauer spectroscopy. Spectra consisting of two sets of octuplets were observed at low temperatures for a neutral MMX chain complex, Pt(2)(dtp)(4)I (dtp = C(2)H(5)CS(2)(-)), with various charge-ordering states at the Pt dimers, indicating that the charge-ordering state is in an alternate-charge-polarization phase (ACP: ...[Pt(2+)-Pt(3+)]-I(0.4-)-[Pt(3+)-Pt(2+)]...I(0.3-)...), which is consistent with a previous low-temperature X-ray diffraction study. The estimated valence states of the bridging iodines of [(C(2)H(5))(2)NH(2)](4)[Pt(2)(pop)(4)I] (pop = H(2)P(2)O(5)(2-)), with a charge-polarization phase (CP: ...[Pt(2+)-Pt(3+)]-I(0.4-)...[Pt(2+)-Pt(3+)]-I(0.4-)...), and [H(3)N(CH(2))(6)NH(3)](2)[Pt(2)(pop)(4)I], with a charge-density-wave phase (CDW: ...[Pt(2+)-Pt(2+)]...I(0.3-)-[Pt(3+)-Pt(3+)]-I(0.3-)...), suggest that the covalent bond interaction is dominant in the CDW phase, whereas the Coulomb interaction is dominant in the CP phase. The estimated absolute quadrupole coupling constant (QCC) values for negatively charged MMX chain complexes with pop ligands are larger than those for neutral MMX chain complexes with CH(3)CS(2)(-) (dta) ligands, implying that the Madelung potential formed by the more-negative pop ligands and countercations effectively contributes to the physical properties of the pop system. The three Pt(III) dimer complexes Pt(2)(dta)(4)I(2), Pt(2)(dtp)(4)I(2), and K(4)[Pt(2)(pop)(4)I(2)] showed almost the same isomer shifts, indicating that the valence state of the iodide ion (I(0.5-)) depends negligibly on the terminal ligand. The QCC value observed for K(4)[Pt(2)(pop)(4)I(2)] was larger than those for Pt(2)(dta)(4)I(2) and Pt(2)(dtp)(4)I(2), originating from the anisotropic arrangement of the iodide anions, which form layers lying on the ab plane in the crystal.