128 research outputs found
Charge and spin state of dilute Fe in NaCl and LiF
There is an apparent mismatch between electron paramagnetic resonance and Mössbauer spectroscopy results on the charge and spin states of dilute Fe impurities in NaCl; Mössbauer spectroscopy data have been interpreted in terms of high-spin Fe2+, while electron paramagnetic resonance studies suggest low-spin Fe1+. In the present study, the charge and spin states of dilute substitutional Fe impurities in NaCl and LiF have been investigated with 57Mnâ57Fe emission Mössbauer spectroscopy. A scheme is proposed which takes into account the effects of nearest-neighbor distances and electronegativity difference of the host atoms on the Mössbauer isomer shift and allows for the unequivocal differentiation between high-spin Fe2+ and high/low-spin Fe1+ in Mössbauer spectroscopy. From these considerations, the Mössbauer results are found to be consistent with dilute Fe impurities in NaCl and LiF in a low-spin Fe1+ state. These conclusions are supported by theoretical calculations of isomer shifts and formation energies based on the density-functional theory. The experimental results furthermore suggest that charge compensation of dilute Mn2+ dopants in NaCl and LiF is achieved by Na vacancies and Fâ interstitials, respectively.We acknowledge the support of the ISOLDE Collaboration and technical teams and cluster resources provided by CERN (HTC/Condor). G. Marschick (Vienna University of Technology, Austria; University Duisburg-Essen, Germany & CERN, Switzerland) is acknowledged for experimental help. B. Qi (University of Iceland, Iceland) is acknowledged for fruitful discussions. S.O. acknowledges support from the University of Iceland Research Fund. R.A. acknowledges the funding of the Austrian Science Fund (FWF) through Projects No. P26830 and No. P31423. The Federal Ministry of Education and Research (BMBF) through Grants No. 05K16PGA and No. 05K19SI1 "eMMA" is acknowledged. The European Commission through the Horizon 2020 programme (Grant No. 654002, ENSAR 2) is acknowledged. K.B.-R., H.M., D.N., K.N., and G.P. acknowledge support of the Department of Science & Innovation (South Africa) within the SA-CERN Program. I.U. acknowledges the support of the Ministry of Economy and Competitiveness (MINECO/FEDER) under Project No. RTI2018-094683-B-C55 and Basque Government Grant No. IT-1500-22
A tentative 4- isomeric state in Sr-98
Annual Report 2001, Institut fuer Kernchemie,
Johannes-Gutenberg-Universitaet, Mainz, GermanyComment: 3 pages, 1 figur
Percolative phase transition on ferromagnetic insulator manganites: uncorrelated to correlated polaron clusters
In this work, we report an atomic scale study on the ferromagnetic insulator
manganite LaMnO using PAC spectroscopy. Data analysis
reveals a nanoscopic transition from an undistorted to a Jahn-Teller-distorted
local environment upon cooling. The percolation thresholds of the two local
environments enclose a macroscopic structural transition
(Rhombohedric-Orthorhombic). Two distinct regimes of JT-distortions were found:
a high temperature regime where uncorrelated polaron clusters with severe
distortions of the MnO octahedra survive up to
and a low temperature regime where correlated regions have a weaker
JT-distorted symmetry.Comment: 4 pages, 4 Figures, submitted to PRL, new version with more data,
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Positron-neutrino correlations in 32Ar and 33Ar Decays: Probes of Scalar weak currents and nuclear isospin mixing
The positron-neutrino correlation in the 0^+ \to 0^+ \beta decay of ^{32}Ar
was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of
the narrow proton group following the superallowed decay. Our result is
consistent with the Standard Model prediction; for vanishing Fierz interference
we find a=0.9989 \pm 0.0052 \pm 0.0036. Our result leads to improved
constraints on scalar weak interactions. The positron-neutrino correlation in
^{33}Ar decay was measured in the same experiment; for vanishing Fierz
interference we find a=0.944 \pm 0.002 \pm 0.003. The ^{32}Ar and ^{33}Ar
correlations, in combination with precision measurements of the half-lives,
superallowed branching ratios and beta endpoint energies, will determine the
isospin impurities of the superallowed transitions. These will provide useful
tests of isospin-violation corrections used in deducing |V_{\rm ud}| which
currently indicates non-unitarity of the KM matrix.Comment: 15 pages, 6 figure
Low-lying levels in Xe
The decays of Cs and Cs to Xe have been studied on mass separated samples, using and internal conversion electron measurements. Several new low-lying levels have been established in the Xe level scheme. Half-life evaluations for Cs and Cs have been revisited. The results are compared with other experimental data known in light odd-mass xenon isotopes and with calculations performed in the frame of the multi-shell interacting boson-fermion model
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