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Combined experiments by 151Eu Mössbauer spectroscopy using a radioactive source, and 151Eu nuclear resonant inelastic scattering (NRIS) and Eu L-edge magnetic circular dichroism (MCD) measurements using synchrotron radiation, were carried out to study the magnetic properties and lattice dynamics in non-doped Eu8Ga15Ge30 and Si-doped Eu8Ga16Ge23Si7 with a type-I clathrate structure. The temperature dependence of MCD signals at the Eu L3-edge agrees with that of magnetization in the ferromagnetically ordered state, contradicting the hypothesis of fluctuating magnetic moments of Eu2+. 151Eu Mössbauer spectra in their ferromagnetic states consist of two components with different hyperfine fields, both of which are smaller than those expected from the full moment of S = 7/2 observed in magnetization measurements. 151Eu NRIS experiments reveal the significant effects of Si doping on the motions of Eu ions, which are attributed to the increased carrier density and chemical pressure effect. [ABSTRACT FROM AUTHOR]

In this publication, the potential non-gadolinium magnetic resonant imaging agent—nanoparticulate K2Mn[Fe(CN)6]—its comparison sample KFe[Co(CN)6], as well as their reference samples were measured and analyzed using Mn, Co and Fe L-edge X-ray absorption spectroscopy (L XAS). From the information obtained, we conclude that K2Mn[Fe (CN)6] has a high spin (hs)-Mn(II) and a low spin (ls)-Fe(II), while KFe[Co(CN)6] has an hs-Fe(II) and an ls-Co(III). In these Prussian blue (PB) analog structures, the L XAS analysis also led to the conclusion that the hs-Mn(II) in K2Mn[Fe(CN)6] or the hs-Fe(II) in KFe[Co(CN)6] bonds to the N in the [M(CN)6]4−/3− ions (where M = Fe(II) or Co(III)), while the ls-Fe(II) in K2Mn[Fe(CN)6] or the ls-Co(III) in KFe[Co(CN)6] bonds to the C in the [M(CN)6]4−/3− ion, suggesting the complexed metalloligand [Mn(II) or Fe(II)] occupies the N-bound site in PB. Then, nuclear resonant vibrational spectroscopy (NRVS) was used to confirm the results from the L XAS measurements: the Mn(II), Eu(III), Gd(III), Fe(II) cations complexed by [M(CN)6]n−-metalloligand all take the N-bound site in PB-like structures. Our NRVS studies also prove that iron in the K2Mn[Fe(CN)6] compound has a 2+ oxidation state and is surrounded by the C donor atoms in the [M(CN)6]n− ions. [ABSTRACT FROM AUTHOR]

149Sm synchrotron-radiation-based Mössbauer spectroscopy has been applied to Sm-based heavy fermion intermetallics, SmTr2Al20 (Tr = Ti, V and Cr) and SmOs4Sb12. The isomer shifts obtained demonstrate that the Sm valence states in these compounds are intermediate. Since the difference of the isomer shifts in 22.502 keV 149Sm Mössbauer effect between Sm2+ and Sm3+ state is comparable to the 2nd order Doppler shift, consideration of the 2nd order Doppler shift is required to precisely discuss Sm valence state through the shifts of the Mössbauer spectra. In addition, the plots of the isomer shifts obtained by the Mössbauer spectroscopy against the Sm valence states estimated from Sm L-edge X-ray absorption spectroscopy exhibit a linear correlation except for that in SmOs4Sb12. This implies that the origin of the intermediate valence state in SmOs4Sb12 differs from that in SmTr2Al20 (Tr = Ti, V and Cr). [ABSTRACT FROM AUTHOR]

Cluster multipole orderings composed of atomic high-rank multipole moments are theoretically investigated with a 5d-electron compound Ca5Ir3O12 in mind. Ca5Ir3O12 exhibits two hidden orders: One is an intermediate-temperature phase with time-reversal symmetry and the other is a low-temperature phase without time-reversal symmetry. By performing the symmetry and augmented multipole analyses for a d-orbital model under the hexagonal point group D3h, we find that the 120°-type ordering of the electric quadrupole corresponds to cluster electric toroidal dipole ordering with the electric ferroaxial moment, which can become the microscopic origin of the intermediate-temperature phase in Ca5Ir3O12. Furthermore, based on 193Ir synchrotron-radiation-based Mössbauer spectroscopy, we propose that the low-temperature phase in Ca5Ir3O12 is regarded as a coexisting state with cluster electric toroidal dipole and cluster magnetic toroidal quadrupole, the latter of which is formed by the 120°-type ordering of the magnetic octupole and accompanies a small uniform magnetization as a secondary effect. Our results provide a clue to two hidden phases in Ca5Ir3O12. [ABSTRACT FROM AUTHOR]

The biological conversion of N2 to NH3 is accomplished by the nitrogenase family, which is collectively comprised of three closely related but unique metalloenzymes. In the present study, we have employed a combination of the synchrotron-based technique of 57Fe nuclear resonance vibrational spectroscopy together with DFT-based quantum mechanics/molecular mechanics (QM/MM) calculations to probe the electronic structure and dynamics of the catalytic components of each of the three unique M N2ase enzymes (M = Mo, V, Fe) in both the presence (holo-) and absence (apo-) of the catalytic FeMco clusters (FeMoco, FeVco and FeFeco). The results described herein provide vibrational mode assignments for important fingerprint regions of the FeMco clusters, and demonstrate the sensitivity of the calculated partial vibrational density of states (PVDOS) to the geometric and electronic structures of these clusters. Furthermore, we discuss the challenges that are faced when employing NRVS to investigate large, multi-component metalloenzymatic systems, and outline the scope and limitations of current state-of-the-art theory in reproducing complex spectra. [ABSTRACT FROM AUTHOR]

We have performed and analyzed the first combined 151Eu and 57Fe nuclear resonant vibrational spectroscopy (NRVS) for naturally abundant KEu(III)[Fe(II)(CN)6] and Eu(III)[Fe(III)(CN)6] complexes. Comparison of the observed 151Eu vs.57Fe NRVS spectroscopic features confirms that Eu(III) in both KEu(III)[Fe(II)(CN)6] and Eu(III)[Fe(III)(CN)6] occupies a position outside the [Fe(CN)6] core and coordinates to the N atoms of the CN− ions, whereas Fe(III) or Fe(II) occupies the site inside the [Fe(CN)6]4− core and coordinates to the C atoms of the CN− ions. In addition to the spectroscopic interest, the results from this study provide invaluable insights for the design and evaluation of the nanoparticles of such complexes as potential cellular contrast agents for their use in magnetic resonance imaging. The combined 151Eu and 57Fe NRVS measurements are also among the first few explorations of bi-isotopic NRVS experiments. [ABSTRACT FROM AUTHOR]

Nuclear resonant vibrational spectroscopy (NRVS) is an excellent synchrotron-based vibrational spectroscopy. Its isotope specificity and other advantages are particularly good to study, for example, iron center(s) inside complicated molecules such as enzymes. In order to investigate some small energy shifts, the energy scale variation from scan to scan must be corrected via an in-situ measurement or with other internal reference peak(s) inside the spectra to be calibrated. On the other hand, the energy re-distribution within each scan also needs attention for a sectional scan which has a different scanning time per point in different sections and is often used to measure weak NRVS signals. In this publication, we: (1) evaluated the point-to-point energy re-distribution within each NRVS scan or within an averaged scan with a time-scaled (not energy-scaled) function; (2) discussed the errorbar contributed from the improper "distribution" of ΔEi or the averaged ΔE within one scan (Eerr1) vs. that due to the different ΔEi from different scans (Eerr2). It is well illustrated that the former (Eerr1) is as important as, or sometimes even more important than, the latter (Eerr2); and (3) provided a procedure to re-calibrate the published NRVS-derived PVDOS spectra in case of need. This article establishes the concept that, at least for sectional NRVS scans, the energy positions should be corrected according to the time scanned rather than be scaled with a universal constant, as in a conventional calibration procedure. [ABSTRACT FROM AUTHOR]

Nuclear resonant vibrational spectroscopy (NRVS) is an excellent modern vibrational spectroscopy, in particular, for revealing site-specific information inside complicated molecules, such as enzymes. There are two different concepts about the energy calibration for a beamline or a monochromator (including a high resolution monochromator): the absolute energy calibration and the practical energy calibration. While the former pursues an as-fine-as-possible and as-repeatable-as-possible result, the latter includes the environment influenced variation from scan to scan, which often needs an in situ calibration measurement to track. However, an in situ measurement often shares a weak beam intensity and therefore has a noisy NRVS spectrum at the calibration sample location, not leading to a better energy calibration/correction in most cases. NRVS users for a long time have noticed that there are energy drifts in the vibrational spectra's zero-energy positions from scan to scan (Δ Ei), but their trend has not been explored and utilized in the past. In this publication, after providing a brief introduction to the critical issue(s) in practical NRVS energy calibrations, we have evaluated the trend and the mechanism for these zero-energy drifts (Δ Ei) and explored their link to the energy scales (αi) from scan to scan. Via detailed analyses, we have established a new stepwise procedure for carrying out practical energy calibrations, which includes the correction for the scan-dependent energy variations using Δ Ei values rather than running additional in situ calibration measurements. We also proved that one additional instrument-fixed scaling constant (α0) exists to convert such "calibrated" energy axis (E′) to the real energy axis (Ereal). The "calibrated" real energy axis (Ereal) has a preliminary error bar of ±0.1% (the 2 σ E divided by the vibrational energy position), which is 4–8 times better than that from the current practical energy calibration procedure. [ABSTRACT FROM AUTHOR]