I.

Project Research
Project 5PR5Project Research on the Advanced Utilization of Multi-Element Mössbauer
Spectroscopy for the Study on Condensed Matter Science

M. SetoResearch Reactor Institute, Kyoto University
OBJECTIVES AND PERFORMED RESEARCHSUBJECTS:
The main objectives of this project research are theinvestigation of the fundamental properties of newmaterials and the development of the advanced
experimental methods by using multi-element Mössbauer
spectroscopy.
Combination
use
of
the
high-magnetic-field superconducting magnet was alsoessential to study the magnetism of the materials. As the
Mössbauer resonance line is extremely narrow, hyperfine
interactions are well resolved and give us the informationon the surrounding electronic states and magnetism. Thus,
the Mössbauer spectroscopy is applied to widely various
areas of researches, such as physical, chemical,
biological,
and
earth
sciences.
Moreover,element-specific or isotope-specific information is one of
the most irreplaceable features of the Mössbauer
spectroscopy. Therefore, promotion of the variety of
Mössbauer isotope provides more useful and valuable
methods for modern precise materials science of complex
systems, such as biological substances, multi-layer films,
and complicated-structured matter.
In this term of the year, some of the planned researches
have not been performed because of the shutdown of theresearch reactor. The research subjects performed are as
follows:
P5-2

Mössbauer microspectrometer using Si-PIN
semi-conductor detector and its application tomineral science (K. Shinoda et al.)

P5-3

57

Fe Mössbauer spectra of Sr2VFeAsO3-d(d=0.232, 0.267, and 0.509) (Y. Kamihara et
al.)

P5-4

Relationship between Heme Electronic Structure
and Oxygen Affinity of Myoglobin (Y.
Yamamoto et al.)P5-8

Development of Mössbauer spectroscopy system
on 67Zn (M. Saito et al.)P5-9

Mössbauer Study of Ba0.6K0.4Fe2As2 under High
Magnetic Fields (S. Kitao et al.)MAIN RESULTS AND CONTENTS OF THISREPORT:
The following reports were contributed by researchgroups in this project research.

28P5

K. Shinoda et al. (P5-2) have developed Mössbauer
microspectrometer using Si-PIN semiconductor detector
and applied to studies of crystallographically-oriented
single crystals of thin sections of augite from different
occurrences. Obtained three sets of quadrupole doublets
were well identified with Fe2+ in M1 and M2 sites, andFe3+ in M1 site in pyroxene structure. From the intensity
ratio of each doublets, the orientation of the electric field
gradient vector was discussed. As a result, goodconcentration of orientation in Fe2+ in M2 site was found,although Fe2+ in M1 site did not show concentration.
Y. Kamihara et al. (P5-3) studied Sr2VFeAsO3-d, which are
related compounds of FeAs-based superconductor withblocking layer and some of which show superconductivity
and antiferromagnetic ordering of Vanadium. Mössbauer
spectroscopy was applied to investigate magnetism of Fe inthese compounds. For the samples with d = 0.232, 0.267,
and 0.509, the spin density wave phase was observed, whilemagnetically-ordered Fe was not observed forsuperconducting Sr2VFeAsO3-d. The result indicates that Fe
has two different magnetic phase, depending on the oxygen
deficiency.
Y. Yamamoto et al. (P5-4) investigated the Mössbauer
spectroscopy to elucidate the relationship between
electronic structure of heme Fe atom and oxygen affinity of
myoglobin(Mb).
Throughthestudiesofchemically-modified heme cofactors, obtained isomer shifts
could not be simply interpreted as the electronic nature of
the hemes. On the other hand, quadrupole splitting values
decreased with decreasing the electron density of the hemes.
These facts are useful to elucidate the electronic structure of
the oxy form of Mb, to understand the oxygenation andautoxidation processes of Mb.
M. Saito et al. (P5-8) attempted to observe the 67Zn
Mössbauer absorption spectrum, which could be useful forexperiments requiring extremely high energy resolution. To
obtain the 67Cu Mössbauer source, ZnO crystals were
irradiated by KURRI-LINAC through photonuclear
reaction. Although measurement of the Mössbauer
spectrum was tried, expected absorption was not observed.
It is considered to be due to the vibrational noise of thevacuum chamber. Further development of the 67Zn
Mössbauer spectroscopic system is in progress.
S. Kitao et al. (P5-9) measured detailed temperaturedependences of Mössbauer spectra under high magnetic
fields to reveal the magnetic properties of the Fe-based
superconductor Ba0.6K0.4Fe2As2. From the temperaturedependence of Mössbauer spectra, small broadening of
the line width were observed at the temperature a little
above the superconducting transition temperature. The
measurements under high magnetic fields revealed theline broadenings are due to quadrupole splittings, whichis consistent to the fact that the electronic nematic states
has the small asymmetry in the structure.

PR5-1

Mössbauer Microspectrometer Using Si-PIN Semi-conductor Detector and its
Application to Mineral Sciences

A. Marutani1, K. Shinoda1, Y. Kobayashi2
1

Department of Geosciences,
Graduate School of Science, Osaka City University
2
Research Reactor Institute, Kyoto University

INTRODUCTION: Mössbauer microspectorometerusing Si-PIN semi-conductor detector was used to measure Mössbauer spectra of single crystals of mineral thinsections. A Pb pin-hole (1mmφ) was used to limit measuring region in a thin section. A Si-PIN semi-conductorof which energy resolution is better than a proportionalcounter is suitable for micro-measurements. Whereas two
peaks' intensity of Q-splitting doublets is equal for powder sample, intensity ratio of Q-splitting doublet of single
crystal varies between 0.6 and 3 depending on the angle
between γ-ray and electric field gradient vector. Augite isa major rock-forming mineral including Fe2+ and Fe3+,and they distribute at M1 and M2 sites in pyroxene
structure. To fitting out M1Fe2+, M2Fe2+ and M1Fe3+
Q-splitting doublets from raw Mössbauer data of single
crystal thin section of augite, orientations of electric field
gradient vector of M1 and M2 sites for Fe2+ and Fe3+ isimportant. In this study, the orientation of electric field
gradient vector of M1Fe2+ and M2Fe2+ were estimated bymeasuring thin sections of augite of which crystal
graphic orientation were determined by X-ray precession
camera.
EXPERIMENTS and RESULTS: Crystal graphicallyoriented thin sections perpendicular to a*- b*- andc*-axes of augite from two different occurrences (Muroto
and Nagasaki) were prepared for Mössbauer microspetrometer. Fig.1 shows Mössbauer spectrum ofaugite thin section perpendicular to a* axis from Na-

28P5-2

gasaki. Two sets of Q-splitting doublets were identified.
The wider Q doublet of 2.08mm/s was assigned to
M2Fe2+ and the narrower doublet of 0.60 mm/s was
M1Fe3+. On the fitting of raw data of Fig.1, the ratio ofintensity of the narrower doublet was fixed to 1:1, andthat of the wider doublet was not fixed and calculated to
0.716. Fig.2 shows Mössbauer spectrum of augite thinsection perpendicular to a* axis from Muroto. three setsof Q-splitting doublets were identified. The first is strong
doublet of 1.97 mm/s Q-splitting which is due to M2Fe2+,
the second is middle doublet of 2.55 mm/s due to M1Fe2+
and weak doublet of 0.61 mm/s due to M1Fe3+. On thefitting of raw data of Fig.2, the ratio of intensity of the
weak doublet was fixed to 1:1, the strong doublet due toM2Fe2+ was fixed to 0.716 from Fig.1 and intensity ratioof middle doublet was not fixed and finally calculated to
1.00. From the relation between the intensity ratio of
doublet (x) and the angle between γ-ray and electric field
gradient vector of augite (θ),

x=

1+ cos2 θ
2 3 + sin 2 θθ of six thin sections were calculated. From the two setsof θs, orientations of electric field gradient vector of
M1Fe2+ and M2Fe2+ of augite were plotted on stereographic projections. As the results, M2Fe2+ shows goodconcentration of orientation, but M1Fe2+ was not show
concentration. To improve data fitting, the proper doublet
parameter of M1Fe3+ must be used.

PR5-2

57

Fe Mössbauer Spectra of Sr2VFeAsO3-d (d = 0.232, 0.267, and 0.509)

Y. Tojo, H. Fujioka, M. Matoba, S. Kitao1, M. Seto1 and
Y. Kamihara
Department of Applied Physics and Physico-Informatics,
Keio University
1
Research Reactor Institute, Kyoto University
Layeredoxypnictide
INTRODUCTION:
Ae2TMFePnO3-d (Ae = Alkaline earth metal, TM = Transition metal) (21113) consists of carrier conducting FePn
(Pn = P and As) layer and carrier blocking Ae2TMO3 layer.
Several 21113 compounds show superconducting phaseat low temperatures. Hyperfine fields (Bhf) measurements
experienced by nuclei of atoms at crystallographic sites
in magnetic and/or antiferromagnetic metals are of interest in view point of hyperfine interactions and important
for their use in the determinations of nuclear magnetic
dipole moments by a variety of methods including those
based on low-temperature nuclear orientation.
Guang-Han Cao et al reported that Sr2VFeAsO3-d is an
FeAs-based layered oxypnictide superconductor, which
exhibits antiferromagnetic ordering under 150 K originating in local d-electron moments of vanadium, and thesuperconducting transition temperature Tc is 24 K.[1,2] In
this study, we focus on magnetic phase of Sr2VFeAsO3-d
as a complex magnetic compounds. [1-8]Element-specific magnetism and electronic phase of Fe
sublattice in Sr2VFeAsO3-d are elucidated using 57Fe
Mössbauer spectroscopy. Studies on hyperfine fields Bhf
experienced by nuclei are of interest in view point ofhyperfine interactions and important for their use in thedeterminations of nuclear magnetic dipole moments.
EXPERIMENTS:
Polycrystalline
samplesof
Sr2VFeAsO3-d were prepared by the solid-state reactions
in a sealed silica tube using dehydrated SrO, FeAs, Vanadium oxides, and V as starting materials. Then, a mixtureof the three powders was pressed into pellet and heated indoubly sealed silica tubes at 1050-1300 °C for 40 h. Allprocedures were carried out in an Ar-filled glove box(MIWA Mfg; O2, H2O < 1 ppm). The crystal phase of theobtained product was examined by powder X-ray diffraction (XRD; RigakuRINT-2500) using CuKα radiation.
Almost all the diffraction peaks are assigned to theSr2VFeAsO3-d phase. Electrical resistivity measurements
were performed at 2–300 K by a dc four-probe techniqueusing silver paste as electrodes. Magnetization measurements were performed for polycrystalline samples using a
Quantum Design magnetic properties measurement system (MPMS). The 57Fe Mössbauer (MS) experiment on
the two series of compounds, Sr2VFeAsO3-d (x = 0.232,
0.267, and 0.509) was performed with conventional 57Fe
MS equipment using 14.4 keV γ-rays from a 57Co sourcein an Rh matrix.
RESULTS: 57Fe MS to the samples of d=0.232, 0.267,
and 0.509 of Sr2VFeAsO3-d were measured and analyzed

28P5-3Fig. 1. 57Fe Mössbauer spectra (MS) of polycrystalline Sr2VFeAsO3-d (d = 0.232, 0.267 and 0.508) atseveral temperatures described in the figure. The
solid lines for each samples are fitted patterns provided that internal magnetic fields with wide distribution exist around 57Fe. Such internal magnetic
field indicate existence of spin density wave in
Sr2VFeAsO3-d (d = 0.232, 0.267 and 0.508).
for obtaining quantitative value of internal magnetic field.
As a result, the existence of spin density wave phaseare observed for x = 0.232, 0.267, 0.509, while magnetic
ordered Fe are not observed for superconducting
Sr2VFeAsO3-d samples.[9] The result indicates that Fe of
Sr2VFeAsO3-d shows two magnetic phase, which stabilities depend on oxygen deficiency.
REFERENCES:[1] X. Zhu, et al., Phys. Rev. B 79, 220512 (2009).
[2] G. H. Cao et al., Phys. Rev. B 82, 104518 (2010).
[3] Y. Kamihara et al., New J. Phys. 12, 033005 (2010).
[4] H. Kotegawa et al., J. Phys. Soc. JPN 78, 123707(2009).
[5] S. Tatematsu, et al, J. Phys. Soc. JPN 79, 123712(2010).
[6] D. Suetin, J. Mater.. Sci. 47, 3663 (2010).
[7] H. Nakamura and M. Machida, Phys. Rev. B 82,
094503 (2010).
[8] Y. Tojo, J. Appl. Phys. 113, 17E157 (2013).
[9] Y. Tojo, et al, unpublished.

PR5-3

Relationship between Heme Electronic Structure and Oxygen Affinity of Myoglobin

K. Hasegawa, M. Saito1, M. Seto1, Y. Kobayashi1, T.
Ohta2, S. Yanagisawa2, T. Ogura2, Y. Yamamoto, T. Shibata, S. Neya3 and A. Suzuki4
Department of Chemistry, University of Tsukuba
1

Research Reactor Institute, Kyoto University
Graduate School of Life Science, University of Hyogo
3
Graduate School of Pharmaceutical Sciences, Chiba
University

2

4

Department of Materials Engineering, Nagaoka National College of Technology

INTRODUCTION: The function of an oxygen storage
hemoprotein, myoglobin (Mb), is regulated through heme
electronic structure, in addition to heme environment
furnished by nearby amino acid residues. We found that adecrease in the electron density of the heme Fe atom (ρFe)
leads to lowering oxygen affinity and a decrease in the
autoxidation rate of the protein.1 These findings could bereasonably explained in terms of the effect of a change inthe ρFe on the resonance A ↔ B of oxy form of Mb (oxyMb) (scheme 1). In this study, we measured Mӧssbauer
spectra of oxyMbs reconstituted with some chemically-modified heme cofactors (Fig. 1) in order to characterize the relationship between the ρFe and the resonanceA ↔ B. The formal charges of heme Fe in the canonicalstructures A and B are +2 and +3, respectively, and hence
the effect of a change in the ρFe on the resonance A ↔ B
could be analyzed through the resonance hybrid of theformal charge of heme Fe which is sharply reflected in
the Mӧssbauer spectral parameters, i.e., isomer shift (IS)and quadrupole splitting (QS).
EXPERIMENTS: ApoMb was prepared from sperm
whale Mb, using the standard procedure, and reconstituted with 57Fe-labelled heme cofactors. 2 mM Mbs in 50
mM potassium phosphate buffer, pH = 7.4, were cooled
rapidly in liquid nitrogen bath. The Mӧssbauer measurements were performed at 3-6 K.

Fig. 1. Chemically-modified heme cofactors used in
the study, and the obtained Mӧssbauer spectral parameters.
RESULTS: The Mӧssbauer spectrum of oxyMb reconstituted with 57Fe-labelled proto (Fig. 2) was almost identical to that previously reported.2 The IS values of theheme cofactors ranged from 0.260 to 0.271 mm/s andcould not be simply interpreted on the basis of the electronic nature of the hemes. On ther other hand, the heme
cofactors were arranged as 2,8-DPF < 7-PF ≈ Proto <3,8-DMD < Meso, in order of increasing QS (Fig. 1),
indicating that the QS decreases with decreasing the ρFe.
This result confirmed that a decrease in the ρFe results in
shifting the resonance A ↔ B toward structure A. Protoand 7-PF exhibited similar QS values, supporting that theρFe values of the two heme cofactors are closely similar toeach other. Thus, Mӧssbauer spectroscopy is a powerfultool to elucidate the electronic structure of oxyMb.
3

436x10Counts

434
432
430
428
426
-4

-2

0

2

4

Velocity(mm/s)

Fig. 2. Mӧssbauer spectrum of oxyMb (proto) at 3 K.

Scheme 1. Oxygenation and autoxidation of Mb, and theresonance structures A and B of oxyMb.

28P5-4

REFERENCES:[1] T. Shibata, D. Matsumoto, R. Nishimura, H. Tai, A.
Matsuoka, S. Nagao, S. Matsuo, S. Hirota, K. Imai, S.
Neya, S. Suzuki, and Y. Yamamoto, Inorg. Chem., 51,(2012) 11955–11960.
[2] B. Boso, P. G. Debrunner, G. C. Wagnner, and T.
Inubushi, Biochem. Biophys. Acta, 791, (1984) 244-251.

PR5-4 Magnetic Property and Local Structures of Functional Irons in Glass by Mössbauer Spectroscopy
N. Umesaki, K. Okada1, Y. Kobayashi 2
Graduate School of Engineering, Osaka University
1
Research & Utilization division, JASRI
2
Research Reactor Institute, Kyoto University
INTRODUCTION and AIM: Glass is used in many
applications in our every-day lives and has new applications. Coexisting divalent iron ions (Fe2+) and trivalentiron ions (Fe3+) in glass affect the transmission from thenear-ultraviolet (NUV) to the near-infrared (NIR) range(hereinafter denoted as “transmission-NUV_NIR”) and coloring (value, chroma, hue) of glass. [1] The transmission-NUV_NIR and coloring determine the utilization purpose of glass in industry. Commercial glass ineluctably
contains very low concentrations of irons (about 0.01-0.1
wt.% iron oxide concentration), which are derived fromraw materials or industrial processes. Higher iron concentration are added by manufacturing design. The ironconcentrations mainly affect the value of coloring. Fe2+
and Fe3+ mainly affect the chroma and hue of coloring.
Fe2+ gives absorption mainly in the NIR range, resulting
in bluish coloring.[1] Fe3+ gives strong absorption mainlyin the visible to NUV range, resulting in yellowish coloring. [1]Two macro parameters have been used in industry tocontrol transmission-NUV_NIR and coloring: (1) the total
iron ion mass concentration in terms of Fe2O3 (hereinafter denoted as “iron oxide concentration; MFe2O3”), and(2) the ratio of the number of Fe2+ to the number of total
irons (hereinafter denoted as “Fe2+/nFe”).
Three dimensional (3D) local structures and propertyof iron ions should also contribute to the transmission-NUV_NIR and coloring. Although many scientists proposed structures of Fe2+ and Fe3+ by traditional measuringmethods, they could not explain the property of irons inglass completely.
By enriching with 57Fe, we made basic soda-lime glass
samples that had 0-0.6 57Fe2+/nFe and MFe2O3 of 0.1, 0.5,
1.5, and 5.0 wt.%.
We have investigated these samples by nuclear resonant inelastic scattering (NRIS) and XAFS methods atsynchrotron radiation, and revealed the 3D local structurearound iron atoms in sub-nanometer region (Okada et al,
submitted to X-ray Spectrometry). And we found the capability of complex magnetic fields of Fe3+ in glass at RT.
Then we have proposed Mössbauer measurements to reveal the magnetic sates and internal magnetic fields from
Fe3+ and Fe2+ atoms, independently, at various temperatures.

with 0.5 wt.% MFe2O3 were measured at RT. As shown in
Fig. 1, there were the differences of continuous components between samples that had different Fe2+/nFe.
These wide structures indicated the local magnetization
around iron atoms. The two Fe3+ components with large
internal magnetic field and the two Fe2+ components withlarge quadrupole splitting have been determined fromtheir isomer shifts by our fittings shown in Fig. 1. And
the results from glass with 0.1-5 wt.% MFe2O3, indicatedthat the Fe3+ and Fe2+ atoms in glass had separate structures. Moreover we measured glass with 0.5 wt.% MFe2O3
and with 0 Fe2+/nFe at 150 K and 70 K. The internal
magnetic field from Fe3+ in the sample was about 51 T
and had internal distribution. We concluded that about
90 % of the Fe3+ in glass had local magnetic order like
antiferromagnetic materials. On the other hand, we concluded that Fe2+ atoms had no magnetic order.

Fig. 1. Mössbauer spectra of glass at RT with 0.5 wt.%
MFe2O3 and with Fe2+/nFe of (a) 0, (b) 0.2, and (c) 0.6.
The dot lines and dot-and-dash lines were fitting
curves from Fe3+ and Fe2+, respectively. The solid line
showed the total fit.

EXPERIMENTS: The measurements were performed
using conventional Mössbauer spectrometer. The specimens for Mössbauer measurements were tuned to 10
mm-phi pellet from the 57Fe enriched glass powders. We
investigated samples at room temperature (RT), 150 K
and 77 K.

Fig. 2. Mössbauer spectra of sample glass at (a) 70 K,(b) 150 K, and (c)R.T. with 0.5 wt.% MFe2O3 and with 0
Fe2+/nFe. Same lines as Fig. 1. The inset panels
showed internal magnetic fields of each temperature.

RESULTS and DISCUSSION: The three glass samples

REFERENCES:[1] F. N. Steele et al., Phys. Chem. Glass. 1965; 6: 246.

28P5-7

PR5-5

Devlopment of Mössbauer Spectroscopy System on 67Zn

M. Saito, Y. Kobayashi, R. Masuda, M. Kurokuzu, S.
Kitao and M. Seto
Research Reactor Institute, Kyoto University
INTRODUCTION: Among various Mössbauer spectroscopy systems, 67Zn Mössbauer spectroscopy systemshows relatively very high energy resolution: the energy
width of the gamma rays is narrow ⊿E ~ 50 peV comparing with the gamma-ray’s energy E0 ~ 93 keV, and therelative energy uncertainty of the gamma rays ⊿E/E0 is
the order of ⊿E/E0 ~ 10-15. [1,2]Therefore, 67Zn Mössbauer spectroscopy system has beenused to study the various physics experiments which require high energy resolution such as the detection of thegravitational red shift of the photons as well as to study
the solid state physics on materials including 67Zn.
However, in spite of its usefulness, only few group succeeded to develop 67Zn Mössbauer spectroscopy so far
owing to its difficulty: the system requires very accurate
control of the relative velocity between the source and theabsorber. Recently, by trial experiment, the Mössbauer
absorption of 67Zn has been observed by authors using
the radioactive Mössbauer source produced by the electron linear accelerator (KURRI-LINAC).
The purpose of this study is to establish the 67Zn Mössbauer spectroscopy system by controlling velocity accurately using a piezo driving system.
67

EXPERIMENTS: In this experiment, the source of Zn
Mössbauer spectroscopy is 67Zn in ZnO mono-crystal
produced by the 68Zn (γ,p) 67Cu reaction using high energy gamma-rays from the platinum target of the LINAC.
The ZnO mono-crystal was irradiated by the high energy
gamma-rays for three days and taken out from the target
room one-day later after the irradiation. The source was,then, annealed at 700 ℃ for 9 hours in Ar atmosphere.
Gamma rays and X rays were detected byGe-semiconductor detector. In Fig. 1, we show the obtained energy spectrum.

Fig. 1. Energy spectrum of radiations from the source.
The 93-keV gamma-rays from 67Zn source could benicely observed and selectively used to obtain the Mössbauer spectrum. The source and the 67ZnO mono-crystal

28P5-8absorber were set to the vacuum chamber and cooled
down to around 10 K. The chamber was put on the vibration-isolated table for the isolation from the external vibration and a piezo driving stage (P752, PI Japan Co.,
Ltd.) was used for a velocity control. Against for the stable absorber, a sinusoidal motion with the amplitude of
12 μm/s was induced to the source.
RESULTS: The obtained 67Zn Mössbauer spectrum isshown in Fig. 2. The velocity calibration was performedby the time dependence of the piezo elongation. The error
bar shows the standard deviation of the obtained value.

Fig. 2. Obtained 67Zn Mössbauer spectrum.
From the previous studies, absorption with the absorption
depth ratio of 0.7 % is expected at zero position of thevelocity.[1] However, from the experiment, the absorption depth ratio is, if any, estimated to be less than 0.1 %.
This result suggests that the strong reduction of the depthof the absorption occurs.
After the experiment, we checked the vibrational noise of
the vacuum chamber by using the laser-Doppler velocimeter. The result suggests that the vibrational noise of
our system is larger than our expectation and too large toobtain the 67Zn Mössbauer spectrum.
From the experiment, we could obtain fundamentally
important knowledge about the current system such as
the gamma-rays count-rate and degree of the external
noise. Based on the obtained knowledge, further development of the 67Zn Mössbauer spectrum is in progress.
REFERENCES:[1] W. Potzel, A. Forster, and G. M. Kalvius, J. Phys.
Colloques 37 (1976) C6-691.
[2] N.N. Greenwood, and T. C. Gibb, “Mössbauer spectroscopy” (Chapman and Hall Ltd., London,1971).

Mössbauer Study of Ba0.6K0.4Fe2As2 under High Magnetic Fields

S. Kitao, M. Kurokuzu, Y. Kobayashi and M. Seto

above Tc. On the other hand, the line width broadening
was not clearly observed below Tc.
When high magnetic fields were applied, the spectra
showed 4-line patterns under the magnetic fields asshown in Fig. 1(b). This pattern can be well understoodas a paramagnetic feature, where the magnetic moments
are entirely aligned to the direction of the applied magnetic fields. However, Mössbauer spectra under the magnetic fields did not show specific broadened feature evenat a little above Tc. Since the spectra did not show broadened magnetically-split spectra, the line broadening due
to small internal magnetic fields was excluded. That is,the broadening may not be originated by internal magnetic fields but by quadrupole splittings. This fact implies
the nature of the nematic phase is due to asymmetry inthe structure. This is consistent with the original findingof the nematic phase due to small structural anisotropy inthe magnetic torque measurements[3].

Research Reactor Institute, Kyoto University

EXPERIMENTS: Ba1-xKxFe2As2 was synthesized byheating of a stoichiometric mixture of ground Ba andFeAs with a little excess of K in a crucible of aluminumoxide sealed in a quartz tube, as in the reported method[2]. The obtained polycrystalline powder was characterized by x-ray diffraction and magnetic susceptibility
measurements. The doping level of x = 0.4 is the optimal
doping, that is, the superconducting transition temperature (Tc) has the maximum value of about 38 K.
57
Fe-Mössbauer spectra were measured using a pellet of
powder sample using a 57Co source in Rh matrix with anominal activity of 1.85 GBq. The velocity scales arereferenced to α-Fe. Magnetic fields were applied by asuperconducting-magnet cryostat with a direction parallelto the γ-rays.
RESULTS AND DISCUSSION: Mössbauer spectra of
Ba0.6K0.4Fe2As2 showed a singlet pattern down to 4.2 K
as in Fig 1(a). This implies the optimally-doped superconductor Ba0.6K0.4Fe2As2 has no magnetic order down to
4.2 K. However, the line width at a little above Tc,
showed a small broadening. This line broadening is considered to be due to the electronic nematic phase at a little

28P5-9

1.00

1.00
0.95

0.98

50K 0T

0.96

50K 14T

0.90
0.94

1.00

1.00

0.95

0.98

40K 0T

0.96

0.90

0.95

40K 14T

0.94
1.00

1.00

0.98

30K 0T

0.96

30K 14T

0.90

0.94
1.00

1.00
0.95

0.98

20K 0T

20K 14T
0.96

0.90

0.94
1.00

1.00

Transmission

INTRODUCTION: After the discovery of so-called“1111” series of Fe-oxipnictide superconductors,
LaFeAsO1-xFx[1], several series of Fe-based superconductors have been extensively investigated. Among related Fe-based superconductors, so-called “122” series
has been of great interest because the superconductivity
emerges with various doping methods. That is, the superconductivity was observed not only with hole doping,Ba1-xKxFe2As2[2] or electron doping, Ba(Fe1-xCox)2As2,
but also with isovalent doping, BaFe2(As1-xPx)2. Recently,
the electronic nematic phase was found in the isovalentdoped BaFe2(As1-xPx)2[3]. This electronic nematic phaseis considered to have an important relationship with superconductivity. The electronic nematic phase was also
found in Ba(Fe1-xCox)2As2. However, it is not clear in thecase of Ba1-xKxFe2As2. Therefore, it is important to investigate the electronic nematic phase in Ba1-xKxFe2As2.
Since 57Fe-Mössbauer spectroscopy is an essential
method to extract the electronic states of Fe, a number of
Mössbauer studies on these Fe-based superconductors
have been carried out and revealed many important facts,
for example, in LaFeAsO1-xFx[4]. Moreover, Mössbauer
spectroscopy under high magnetic fields has advantageous to reveal the nature of magnetism in these compounds[5]. In this study, detailed temperature dependences of Mössbauer spectra under high magnetic fields
were measured to investigate the properties of the electronic nematic phase.

0.95

Transmission

PR5-6

4.2K 0T

0.90
0.85
0.80

0.98
0.96

4.2K 14T

0.94
0.92

BaKFe2As2
x=0.4

0.90
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Velocity (mm/s)

2

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BaKFe2As2
x=0.4
-2

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4

Velocity (mm/s)

Fig. 1 Typical Mössbauer spectra of Ba0.6K0.4Fe2As2(a)without magnetic fields and (b)under magnetic fieldsof 14T.
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