PR13

Project Research on the Advanced Utilization of Multi-Element Mössbauer
spectroscopy for the Study of Condensed Matter

M. Seto

MAIN RESULTS AND CONTENTS OF THISREPORT: The following reports were contributed byresearch groups in this project research.

Research Reactor Institute, Kyoto University

T. Okano et al. (P13-2) have measured 57Fe Mössbauer
spectra of Cr-doped CeFePO, for which they
demonstrated a novel ferromagnetic QCP. From theobtained spectra, they showed that transition metal Cr
substitution for Fe in CeFePO gradually generates a FM
ordering of Ce sublattice and suppresses theferromagnetic ordering by further doping, whereas Fe
sublattice does not show magnetic ordering.
197
T. Yokoyama et al. (P13-3) performed Au Mössbauer

OBJECTIVES AND PERFORMED RESEARCHSUBJECTS: Mössbauer spectroscopy is a powerful andwell established method in a wide variety of researchareas, such as physical-, chemical-, biological-, andearth-sciences. As the Mössbauer resonance line isextremely narrow, hyperfine interactions are wellresolved and give us the information on the surrounding
electronic states and magnetism. The element specificinformation, which is one of the most superior features ofthe Mössbauer spectroscopy, is important and required
for modern precise materials science and complex
systems such as biological substances. Moreover,
Mössbauer spectroscopy is useful and valuable because it
usually does not demand the doping of radioactive
sources for the measured samples; the decay of theunstable nucleus sometimes induces the unwanted changeof local electronic states.
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 under high-magnetic fields.
However, owing to the unexpected shutdown of theresearch reactor and the tracer laboratory for the long term,some of the planned researches have not been performed.
The research subjects performed are as follows:

P13-2
P13-3

P13-5
P13-6

P13-7
P13-9

spectroscopic study of manganese dioxides, and theinformation obtained from the analysis of the measured

spectra indicated a formation of Au(III) surface complex
on manganese dioxide.
To investigate the origin of the multiferroics and identify
phase relation in the ferroelectric catalysis, S. Nakamura
et al. (P13-5) studied spinel type FeCr2O4 and Sn/BaTiO3
as multiferroics and ferroelectric catalysis, respectively.
From the 57Fe Mössbauer spectrum of FeCr2O4 at 4.2 K in
applied magnetic field of 2T and the 119Sn Mössbauer
spectrum of Sn/BaTiO3 specimen at room temperature,
the electronic states relevant to multiferroics werediscussed.
T. Kamiryo, et al. (P13-6) measured Mössbauer spectra oforiented thin sections of natural magnetite to observe thedependence of absorption peak intensities on the
crystallographic orientation, and the proposed model
were discussed to explain the result.
To develop zero thermal expansion (ZTE) materials, I.
Yamada et al. (P13-7) studied the chemical substitution
effect of cubic perovskite oxide LaCu3Fe4O12 on thermal
expansion property by X-ray diffraction, thermal analysis,
and Mössbauer spectroscopy, and the obtained results
indicate that the unusual thermal expansion properties of
LaCu3Fe4–xMnxO12 are associated with valence transitionsof Fe ions.
To understand the nature of the Fe-oxipnictide
superconductors, S. Kitao et al. (P13-9) studied themagnetic
properties
oftheoptimally-doped
superconductor Ba0.6K0.4Fe2As2, and under-doped
superconductor Ba0.8K0.2Fe2As2 using Mössbauer
spectroscopy. From the obtained spectra, the co-existenceof magnetism and superconductivity was not observed in
the optimally-doped Ba0.6K0.4Fe2As2. On the other hand,
Mössbauer spectra of under-doped Ba0.8K0.2Fe2As2
showed magnetic order below around 100 K, implyingthat the superconductivity and magnetic order co-exist.

Magnetism of an iron oxypnictide Cr-doped
CeFePO (T. Okano et al.).
A study of formation of Au(III) surface complex
on manganese dioxide by 197Au Mössbauer
spectroscopy (T. Yokoyama et al.).
Mössbauer Spectroscopy of Novel FerroelectricMaterials (S. Nakamura, et al.).
Mössbauer spectra of oriented thin sections andsmall grain of magnetite single crystal(T. Kamiryo, et al.).
Electronic States of Negative/Zero Thermal
Expansion Materials (I. Yamada et al.).
Mössbauer Study of Fe-Based Superconductors,
Ba1-xKxFe2As2 (S. Kitao, et al.).

採択課題番号 26P13（京大・原子炉）瀬戸

多元素メスバウアー分光法の凝縮系研究への高度応用

誠75

プロジェクトMagnetism of an Iron Oxypnictide Cr-doped CeFePO

T. Okano, M. Matoba, Y. Sakai, A. Sakurai, H. Fujioka, A.
Wakatuki, K. Takeuchi, K. Nagamine, S. Kitao1, M. Seto1,
and Y. Kamihara(b) 1.00

(a)
1.00

300 K

0.90
300 K

1.00

Transmission

30 K

Department Applied Physics and Physico-Informatics,
Keio University
1
Research Reactor Institute, Kyoto University
INTRODUCTION: A continuous phase transition,
which is stimulated by an external pressure, magnetic
field, and/or chemical doping at zero temperature, iscalled a quantum phase transition (QPT). The criticalpoint of QPT is called a quantum critical point (QCP),
where second-order phase transitions have been suppressed to zero from finite temperatures. QCPs have attracted much attention since some materials exhibit superconductivity in chemical compositions proximity to a
QCP. [1–5] An iron oxypnictide CeFePO is a related
compound of an iron-based superconductor LaFePO [6]CeFePO is also one of heavy-fermion materials with Ce.
4f-electron’s sublattice inducing Kondo screening. [7,8]In the case of Ruderman-Kittel-Kasuya-Yosida (RKKY)
exchange interaction exceeding Kondo screening, longrange magnetic order appears. While many Ce-based
Kondo lattices show antiferromagnetic (AFM) groundstates, only few systems are known with ferromagnetic(FM) order competing Kondo screening. In CeFePO,
magnetic ordering is almost quenched and/or suppressed.
[8] For Cr-doped CeFePO, we demonstrate a novel ferromagnetic QCP. [1] These ferromagnetic metals are ofinterest 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.
EXPERIMENTS: Polycrystalline CeFe1-xCrxPO (x =0.000–0.692) were prepared by a solid state reaction.
Samples were characterized by X-ray diffraction (XRD),
magnetization measurements, and 57Fe Mössbauer spectroscopy (MS) at various temperatures. Magnetization
measurements were performed on a superconducting
quantum interference device (SQUID).
RESULTS:
Almost all XRD diffraction peaks are assigned to calculated Bragg positions of the CeFePO phase with spacegroup P4/nmm (No. 129), although there are several
weak peaks which can be attributed to Cr2P, Ce2O3, andCeO2. These impurities provide no significant influenceon magnetic measurements of CeFe1-xCrxPO because it
has been confirmed that they do not show ferromagnetic
phase down to 2 K. Samples contained less than 1 at.% of
Cr2P and 2 at.% of Ce2O3 for x = 0.500. However, forx>0.500, a ratio of Ce2O3 phase increases rapidly andCeO2 phase emerges. Figure 1 shows 57Fe MS of x = 0.10

0.90

1.00
4.2 K

Transmission

PR13-1

0.90
1.00
20 K

0.90
1.00
10 K

0.90
0.90
1.00

0.80

4.2 K

-4

-2

0

2

-1

Velocity (mm s )

4

0.90

-4

-2

0

2

-1

4

Velocity (mm s )Fig. 1 Observed 57Fe MS of x = 0.100 (a), 0.200 (b)for CeFe1-xCrxPO at several temperatures. Each solidline is a theoretical spectrum that includes a finite
quadrupole splitting. All MS can be fitted with nomagnetic splitting indicating paramagnetic phase of
Fe sublattice.
and 0.20 for CeFe1-xCrxPO from 4.2 K to 300 K. Our results show that transition metal Cr substitution for Fe in
CeFePO gradually generates a FM ordering of Ce
sublattice and suppresses the FM ordering by further
doping, whereas Fe sublattice does not show magnetic
ordering. The ground state of Ce 4f orbital in CeFePO is
dependent on interlayer distances.[9] Arrott plot of theM-H curves determines a ferromagnetic transition temperature (Tc) for Cr-doped CeFePO. [1]
REFERENCES:[1] T. Okano, S. Kitao, M. Seto, T. Atou, M. Itoh, M.
Matoba, and Y. Kamihara, J. Appl. Phys., 117 (2015)
17E123/1-4.
[2] C. Krellner, K. S. Kini, E. M. Brüning, K. Koch, H.
Rosner, M. Nicklas, M. Baenitz, and C. Geibel, Phys.
Rev. B, 76 (2007) 104418.
[3] E. M. Brüning, C. Krellner, M. Baenitz, A. Jesche, F.
Steglich, and C. Geibel, Phys. Rev. Lett., 101 (2008)
117206/1-4.
[4] S. Doniach, Physica B+C, 91 (1977) 231-234.
[5] K. Yoshida, A. Okiji, Prog. Theor. Phys., 34 (1965)
505-522.
[6]Y. Kamihara, H. Hiramatsu, M. Hirano, R. Kawamura,
H. Yanagi, T. Kamiya, and H. Hosono, J. Am. Chem.
Soc., 128 (2006) 10012-10013.
[7] T. Nakamura, T. Yamamoto, M. Matoba, Y. Einaga,
and Y. Kamihara, J. Phys. Soc. Jpn., 81 (2012)
064714/1-4.
[8] S. Kitagawa, H. Ikeda, Y. Nakai, T. Hattori, K. Ishida,
Y. Kamihara, M. Hirano, and H. Hosono, Phys. Rev.
Lett., 107 (2011) 277002/1-5.
[9] S. Kitagawa, K. Ishida, T. Nakamura, M. Matoba, and
Y. Kamihara, J. Phys. Soc. Jpn., 82 (2013) 033704/1-4.

採択課題番号 26P13-2
ペロブスカイト関連鉄系超伝導体の磁性
プロジェクト(慶大・理工) 岡野智宏、的場正憲、酒井雄樹、櫻井信、藤岡弘考、若月厚志、竹内勝彦、長嶺良麿、神原陽一 (京大・原子炉）北尾真司、瀬戸誠

76

PR13-2

A study of formation of Au(III) surface complex on
manganese dioxide by 197Au Mössbauer spectroscopy

T. Yokoyama1, Y. Okaue1, D. Kawamoto1, H. Ando1, H.
Ohashi2, S. Kitao3 and Y. Kobayashi3

may be fixed tightly on the surface of MnO2 due to theformation of Au-O-Mn bond (surface complex).
In conclusion, information arising from the analysis of197
Au Mössbauer spectroscopy indicated Au(III) ion adsorbed chemically to form surface complexes before
spontaneous reduction of the Au(III) to Au(0).

1Faculty of Sciences, Kyushu University
Faculty of Arts and Science, Kyushu University
3
Research Reactor Institute, Kyoto University
2

INTRODUCTION: It is known that gold nanoparticles
supported on metal oxide have been used as various oxidation-reduction catalysts. Gold catalyst made by deposition-precipitation (DP) method has been often used forcatalytic study. However, it has been still poorly understood how Au(III) ions are precipitated on the surface of
metal oxide. We have studied for Au(III) ions adsorption
on the surface of metal oxide. In our study, we concluded
that adsorbed Au(III) ions were not physically adsorption
but chemical adsorption with surface complex (M－O－
Au, M:metal). We did not prove straightforwardly theformation of Au(III) surface complex on metal oxide,
which the aim of this study is to prove by means of 197Au
Mössbauer spectroscopy.

1.00
0.99
0.98

Relative Transmission

EXPERIMENTS: Au(III) ion adsorbed on manganeseoxide was prepared by batch method. Manganese dioxide (Chuo Denki Kogyo Co., Ltd.) was added into An
aqueous solution of HAuCl4 under stirring and maintaining pH 6. The suspended solution was filtered with 0.45
μm membrane filter.
The chemical state of gold in the solid samples obtained was determined by 197Au Mössbauer spectroscopy(home-made equipment). The 197Pt isotope (T1/2 = 18.3h), γ-ray source feeding the 77.3 keV Mössbauer transition of 197Au, was prepared by neutron irradiation of isotopically enriched 196Pt metal at the Kyoto University
Reactor. The absorbers were particle specimens. The
source and specimens were cooled with a helium refrigerator. The temperature of the specimens was in therange 8 – 15 K. The zero velocity point of the spectra
was the peak point of pure bulk gold. The spectra for all
the solid samples were fitted to a single Lorentzian function.

1.00

0.99

(b)

1.00

0.99

(c)

0.98

-15 -10 -5 0
5 10 15
Velocity / mm s-1

20

Fig. 1. 197Au Mössbauer spectra for Auad/MnO2(a),KAuBr4(b) and AuMe2acac(c).

Au/MnO2RESULTS: Figure 1 shows 197Au Mössbauer spectra ofstandard materials and Au(III) adsorbed on manganesedioxides. Figure 2 shows relative absorption area estimated from spectra in Fig.1 based on area of gold plate.
The area is a measure of the recoilless fraction which is afunction of the degree of fluctuation of Au nuclei (structural hardness). In Fig. 2, area of KAuBr4 is considerably smaller than that of Auad/MnO2. The result suggeststhat Au nuclei in KAuBr4 can fluctuate more easily thanthat in Auad/MnO2, deducing that the latter Au(III) ion

採択課題番号 26P13-3

(a)

0.97

KAuBr4

AuMe2acac

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Normalized Area ratio (gold plate =1.0)

Fig. 2. Normalized area ratio of 197Au Mössbauer
spectra for AuMe2acac, KAuBr4 and Auad/MnO2.

メスバウアー分光による金属酸化物上に吸着した金(III)イオンの触媒的還元反応の状態分析

プロジェクト（九大院・理）横山拓史、岡上吉広、川本大祐、安東宏晃 （九大・基幹教育院）大橋弘範（京大・原子炉）北尾真司、小林康浩
77PR13-3

Mössbauer Spectroscopy of Novel Ferroelectric Materials

S. Nakamura, J. Kano1, N. Oshime1, N. Ikeda1, Y. Kobayashi2, S. Kitao2 and M. Seto2

with the estimated direction of the magnetic moments.
Note that the quadrupole splitting e2qQ/2 changes from
-3.11 (Hex = 0) to -3.23 mm/s (Hex = 2 T), which may be
indicative of the multiferroelectricity of this material.
In Fig. 2, 119Sn Mössbauer spectrum of Sn/BaTiO3
specimen at room temperature is shown. The spectrum iscomposed of a quadrupole doublet with isomer shift of-0.015 mm/s and quadrupole splitting of 0.519 mm/s.
Thus we can identify that the supported Sn is in the formof SnO2. The absorption line width is rather large (0.879mm/s), which is a result of a distribution in quadrupole
splitting due to the particle size of nanometers.

Department of Science and Engineering, Teikyo University
1
Graduate School of Natural Science and Technology,
Okayama University
2
Research Reactor Institute, Kyoto University
INTRODUCTION: Recently, novel materials related
to ferroelectrics have attracted much interest. One example is multiferroics that has at the same time ferromagnetic (or antiferromagnetic) order and ferroelectric order.
The other example is ferroelectric catalysis that is composed of metal nanoparticles supported on ferroelectric
particles. In order to investigate the origin of the multiferroics, or identify phase relation in the ferroelectric catalysis, Mössbauer spectroscopy is a useful probe [1-6].
In this research, we deal with a spinel type FeCr2O4 and
Sn/BaTiO3 as multiferroics and ferroelectric catalysis,
respectively. FeCr2O4 reveals a ferrimagnetic order below
around 70 K (tetragonal phase), followed by a spiralmagnetic order below 35 K (orthorhombic phase). In the
spiral magnetic state, a multiferroic state is expected. On
the other hand, Sn/BaTiO3 is expected as a new catalyst
for the exhaust emission. The phase relation of the supported Sn compound was not clear, because its amount is
too little to be identified by usual X ray diffraction.

4

absorption intensity (count)

2.7 104

2.6 10S1
S2

4

2.5 10FeCr2O4
T = 4.2 K, Hex = 2 T

4

2.4 10-10-50v (mm/s)5

10absorption intensity (count)Fig.1 57Fe Mössbauer spectrum of FeCr2O4 at 4.2 K
in applied magnetic field of 2 T.

EXPERIMENTS:
For FeCr2O4, a single crystal
specimen of (100) platelet was used as an absorber. In
order to obtain a single domain state in the low temperature phases, a slight compression along [001] axis wasadded by attaching epoxy resin on its both edges. 57Fe
Mössbauer spectroscopy was conducted in conventionaltransmission geometry by using 57Co-in-Rh (50 mCi) as γ
ray source. The spectrum was measured at 4.2 K withapplication of a magnetic field of 2 T. The direction ofthe γ ray and the magnetic field were parallel to the [100]axis. While for Sn/BaTiO3, a powder specimen was used
as an absorber. 119Sn Mössbauer spectroscopy was conducted by using 119Sn-in-CaSnO3 (20 mCi) as γ raysource. The spectrum was measured at room temperature.

5.6 106

5.55 106

5.5 1065.45 106

5.4 106

Sn/BaTiO3
at RT

-4

-3

-2

-1

0
1
v (mm/s)2

3

4

Fig. 2 119Sn Mössbauer spectrum of Sn/BaTiO3
specimen at room temperature
REFERENCES:[1] S. Nakamura et al., J. Phys. Conf. Ser. 200, 012140(2010).
[2] S. Nakamura et al., J. Phys. Soc. Jpn. 83, 044701(2014).
[3] S. Nakamura et al., J. Phys. Soc. Jpn. 84, 024719(2015).
[4] S. Nakamura et al., J. Phys. Conf. Ser. 592, 012122(2015).
[5] T. Okamoto et al., Hyperfine Interactions 219,147-152 (2013).
[6] J. Kano et al., Jpn. J. Appl. Phys. 53, 05FB24 (2014).

RESULTS: In Fig. 1, 57Fe Mössbauer spectrum of
FeCr2O4 at 4.2 K in applied magnetic field of 2 T isshown. The spectrum is composed of two subspectra,
which indicates that the magnetic structure is not a simple
cone spiral type. Although both magnetic moments lie
approximately in the orthorhombic c-plain, one is directed along the a-axis (corresponding to the cubic [100]),
whereas the other inclines about 60º from the a-axis. The
observed fields (Hobs) decrease by 2 and 1 T, respectively,
due to the applied magnetic field. This is well consistent

採択課題番号 26P13-5
新規誘電体関連材料のメスバウアー分光
プロジェクト（帝京大・理工）中村真一（岡大・自然）狩野旬、押目典宏、池田直（京大・原子炉）瀬戸誠、北尾真司、小林康浩
78

PR13-4

Mössbauer Spectra of Oriented Thin Sections andSmall Grain of Magnetite Single Crystal

T. Kamiryo, K. Shinoda, Y. Kobayashi1
The following two models were discussed to explain thisresult. In the first model, supposing that magnetic domains with the easiest magnetization axis of crystallographically equivalent <100> or <110> or <111> arepresent equally in oriented thin sections, the peak 2 ration
were always 2 in all cases. This model is not consistent
with this result. In the second model, supposing shapemagnetic anisotropy, which means possibly high magnetic domains with the magnetized orientation parallel tothe thin sections and low magnetic domains normal to thethin sections, this result can be explained only by the<111> easiest magnetization axis. This is consistent
with the general easiest magnetization axis of spinel ferrite.

Department of Geosciences,
Graduate School of Science, Osaka City University
1
Research Reactor Institute, Kyoto University

INTRODUCTION: We have made Mössbauer micro-spectrometer using a multi-capillary X-ray lense(MCX) and estimated beam size of γ-ray at the focus inorder to measure Mössbauer spectra of a single crystal in
petrographic thin sections (KURRI Progress Report2013). As powdered crystals are generally used forconventional Mössbauer spectroscopy, anisotropy of
crystal against incident γ-ray can be cancelled by randomorientation of powders, and sextet peaks due to internal
magnetic field are averaged into intensity ratio of
3:2:1:1:2:3. On the other hand, intensity ratio of sextet
of single crystal depends on the crystal orientation. In
this study, to observe crystallographic orientational dependence of sextet, Mössbauer spectra of oriented thinsections of natural magnetite were measured.

Mössbauer spectra measurements of small single grainsof magnetite with MCX were not done, because theTracer Laboratory was not opened for Mössbauer
specrtroscopy.

EXPERIMENTS and RESULTS: Two natural magnetite single crystals were prepared. Using X-ray precession camera, (100), (110) and (111) oriented thin sections
were made for Mössbauer spectra measurements. Vacancy x (Fe3-xO4, 0<x<0.33) of Brazil and Russia magnetites was estimated to approximately 0 and 0.2, respectively, from Mössbauer spectra. Peak fittings as two
sets of sextet were done for 6 thin sections. Sextet of
49T and 46T magnetic fields are shown in table as Fe3+
and Fe2.5+, respectively. Relative intensity in the table isthat of the second peak (peak 2) against the third peak
(peak 3) among separated 6 peaks. For powdered magnetites, the relative intensity of peak 2 is always 2. But
they were deviated from 2 due to crystal anisotropy.

occurrence
BrazilRussiaindex Fe2.5+ Fe3+(100) 1.96

1.72(110) 2.70

2.31(111) 2.86

2.56(100) 1.98

1.83(110) 2.73

2.64(111) 2.75

2.63

Table. Relative intensity of peak 2 against peak 3 among
sextet of magnetite.

採択課題番号 26P13-6 磁鉄鉱定方位単結晶と単粒結晶のメスバウアースペクトル測定 プロジェクト（大阪市大・理）上領卓也、篠田圭司（京大・原子炉）小林康浩	
 79

PR13-5

Electronic States of Negative/Zero Thermal Expansion Materials

I. Yamada,1 S. Marukawa,2 S. Kitao3, and M. Seto3
1

Research Institutes for the Twenty-First Century
Osaka Prefecture University
2
Department of Chemistry, Osaka Prefecture University
3
Research Reactor Institute, Kyoto University
INTRODUCTION: Positive thermal expansion (PTE)
is an essential property of materials. A limited number ofmaterials shrink with heating, which is described as negative thermal expansion (NTE). NTE property contributes
to development of zero thermal expansion (ZTE) materials, in which the thermal expansion coefficient is almost
zero. ZTE materials are desired in a wide range of applications such as precise mechanics, optics, and electronics.
We investigated the chemical substitution effect of cubic
perovskite oxide LaCu3Fe4O12 on thermal expansion
property by X-ray diffraction, thermal analysis, andMössbauer spectroscopy. Eventually, we obtained almost
ZTE in Mn-doped sample, LaCu3Fe4–xMnxO12 [1].

Fig. 1. Temperature dependence of the unit cellvolume for LaCu3Fe4–xMnxO12.

EXPERIMENTS: LaCu3Fe4–xMnxO12 samples weresynthesized under high-pressure and high-temperature
conditions of 15 GPa and 1473 K, respectively. Synchrotron X-ray powder diffraction (SXRD) data were collected at temperatures between 100 and 450 K at theBL02B2 beamline of SPring-8. 57Fe Mössbauer spectroscopy measurements were conducted at temperaturesin transmission geometry using 57Co/Rh as a radiation
source.
RESULTS: Fig. 1 shows temperature dependence of
the unit cell volume for LaCu3Fe4–xMnxO12. A systematic
trend from abrupt volume expansion/shrinkage (x =0–0.5), NTE (x = 0.75), ZTE (x = 1), and PTE (x = 1.5)
was confirmed [1]. This indicates that the thermal expansion properties of this system are adjustable by chemical
doping. Fig. 2 shows Mössbauer spectra of the x = 0.75
and 1 samples collected at temperatures between 77 and
320 K. Nonmagnetic component are predominant above
room temperature whereas magnetically split sextets are
predominant at 77 K. The isomer shift values increased
by ~0.05 mm/s at magnetic transition temperatures,
which is attributed to the Fe valence reduction by intersite charge transfer (Cu2+ + Fe4+ ⇄ Cu3+ + Fe3+). These
results indicate that the unusual thermal expansion properties of LaCu3Fe4–xMnxO12 are associated with valencetransitions of Fe ions.
REFERENCES:[1] I. Yamada et al., Appl. Phys. Lett., 105 (2014)
231906.

Fig. 2. Mössbauer spectra of LaCu3Fe4–xMnxO12 (x= 0.75, 1).

採択課題番号 26P13-7	 メスバウアー分光法を用いたプロジェクト異常高原子価Feペロブスカイト酸化物の電子状態解明	
 (大阪府大・21 機構)山田幾也（大阪府大・院理）丸川翔平（京大・原子炉）北尾真司、瀬戸誠	
 80

PR13-6

Mössbauer Study of Fe-Based Superconductors, Ba1-xKxFe2As2

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

RESULTS AND DISCUSSION: Typical Mössbauer
spectra for BaFe2As2 are shown in Fig. 1. The magnetictransition was clearly observed by the temperature dependence of the Mössbauer spectra. The observed internal magnetic field reached around 5.4 T at 2.5 K. The
magnetic transition was clearly observed at around 150 K.
These values well agreed with the former report[5].
On the other hand, Ba0.6K0.4Fe2As2 showed only a single
peak spectrum down to 4 K, implying no magnetic transition occurs in optimally-doped superconductor. Thus, theco-existence of magnetism and superconductivity was notobserved in the optimally-doped Ba0.6K0.4Fe2As2. This
fact was similar to the “1111” compound,
LaFeAsO1-xFx[4]. However, Mössbauer spectra in under-doped Ba0.8K0.2Fe2As2 showed magnetic order below
around 100 K, implying that the superconductivity andmagnetic order co-exist in the under-doped
Ba0.8K0.2Fe2As2. This co-existence in some of Fe-based
superconductors is still one of the main controversial
issues. Further Mössbauer study will be performed toinvestigate this issue.

Research Reactor Institute, Kyoto University
INTRODUCTION: After the discoveries of theso-called “1111” series of Fe-oxipnictide superconductors,
LaFePO[1] and LaFeAsO1-xFx[2], several series of
Fe-based superconductors have been successively discovered and extensively investigated to elucidate themechanism of their superconductivity. Among the related
Fe-based superconductors, the so-called “122” series has
been found by K-doping (i.e. hole-doping) of
BaFe2As2[3]. This series has become one of the maingroups of Fe-based superconductors, since the various
superconductors have been found not only byhole-doping but by electron-doping and even by isovalent
doping. Such variety of superconductors provides complexity in the understanding of the mechanism of superconductivity, since the character of each Fe-based superconductor shows various different properties.
To promote the understanding of the superconducting
mechanism, studies of their Fe magnetism is one of themain approaches, since it is supposed that the Fe acts as a
key element and that the magnetism must relate to thesuperconductivity. To investigate the nature of its magnetism, 57Fe-Mössbauer spectroscopy is an essential
method. Until today, a number of Mössbauer studies onthese Fe-based superconductors have been carried out
and revealed many important facts, for example, that thesuperconductivity and magnetic order do not co-exist in
LaFeAsO1-xFx[4]. However, in Ba1-xKxFe2As2, unlike
LaFeAsO1-xFx, it is known that the superconductivity andmagnetic order co-exist in some doping region of theunder-doped Ba1-xKxFe2As2[5].
In this study, a detailed temperature dependence of
Mössbauer spectra was measured to investigate the magnetic properties of the parent compound, BaFe2As2, optimally-doped superconductor, Ba0.6K0.4Fe2As2, and under-doped superconductor, Ba0.8K0.2Fe2As2.

REFERENCES:[1] Y. Kamihara, H. Hiramatsu, M. Hirano, R. Kawamura, H.
Yanagi, T. Kamiya and H. Hosono, J. Am. Chem. Soc. 128(2006)10012.
[2] Y. Kamihara, T. Watanabe, M. Hirano and H. Hosono, J. Am.
Chem. Soc. 130 (2008) 3296.
[3] M. Rotter, M. Tegel, and D. Johrendt, Phys. Rev. Lett. 101(2008) 107006.
[4] S. Kitao, Y. Kobayashi, S. Higashitaniguchi, M. Saito, Y.
Kamihara, M. Hirano, T. Mitsui, H. Hosono and M. Seto, J.
Phys. Soc. Jpn. 77 (2008) 103706.
[5] M. Rotter, M. Tegel, I. Schellenberg, F. M. Schappacher, R.
Pöttgen, J. Deisenhofer, A. Günther, F. Schrettle, A. Loidl
and D. Johrendt, New J. Phys. 11 (2009) 025014.

1.00

1.00

120K

0.98

EXPERIMENTS: BaFe2As2 was synthesized by heatingof a stoichiometric mixture of ground Ba and FeAs in a
crucible of aluminum oxide sealed in a quartz tube, as in
the reported method[3]. K-doped Ba1-xKxFe2As2 wassynthesized similarly, except that excess amount of K
was added and heated in lower temperature. The obtainedpolycrystalline powder was characterized by x-ray diffraction and magnetic susceptibility measurements. The
superconducting
transition
wasobserved
inBa0.6K0.4Fe2As2 and Ba0.8K0.2Fe2As2 at around 30 to 40 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.

0.98

300K

0.96
1.00

100K

0.98

1.00
0.98

150K

0.96
0.96
1.00

1.00

77K

0.98

0.98

140K

0.96

Transmission

0.96
1.00

1.00

2.5K

0.98

130K

0.98
0.96

0.96

0.94

BaFe2As2
-3

-2

-1

0

1

Velocity (mm/s)

Fig. 1.

2

3

-3

-2

-1

0

1

2

3

Velocity (mm/s)

Typical Mössbauer spectra of BaFe2As2.

採択課題番号 26P13-9 多元素メスバウアー分光法を用いた新規材料の物性研究
プロジェクト（京大・原子炉）北尾真司、小林康浩、齋藤真器名、増田亮、黒葛真行、瀬戸誠、窪田卓見
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