実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF	 Experimental Report

提出日 Date of Report
30 March 2015

課題番号 Project No.

装置責任者 Name of responsible person

2014A0187

Yasuhiro Miyake

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）µSR study of the magnetism and superconductivity in H-substituted

MUSE D1

Fe-based superconductor CeFeAsO1-xHx

実施日 Date of Experiment

実験責任者名 Name of principal investigator

22-26 June 2014

Masatoshi Hiraishi
所属 Affiliation
Institute of Materials Structure Science, KEK
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.

Chemical formulas

Physical form.

Mass / g

CeFeAsO0.62H0.54

Pelletized polycrystal

1.0

CeFeAsO0.36H0.62

Pelletized polycrystal

1.0

CeFeAsO0.34H0.66

Pelletized polycrystal

1.0

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

We perfomed muon spin relaxation (µSR) measurements at MUSE D1 area of MLF J-PARC on CeFeAsO1-xHx(Ce1111-H) with x = 0.54, 0.62, and 0.66 to investigate the magnetic ground state of the highly doped region. Astandard zero field (ZF) µSR method using intense surface muon beam under the 300kW MLF beam power wasconducted. Pellet shaped polycrystalline samples were mounted on the 15 x 15 or 20 x 20 mm2 Ag sampleholder, which is cooled by thermal conduction from the cryostat.
It is revealed that ZF-µSR time spectra of Ce1111-H with x = 0.54, 0.62, 0.66 below 100 K exhibit apparent
reduction of the initial asymmetry A0 compared to the spectrum above 100 K, as shown in Fig. 1 (a, b, c),indicating that spatial segregation of non-magnetic and magnetic phases occurs with decreasing temperature.
Due to the limitation of the instrumental time resolution, fast relaxation/rotation signal from the magnetic phaseresults in disappearance of the A0. Moreover, spectra above magnetic transition temperature (TN) exhibit
x-independent exponential depolarization, which is currently attributed to Lorentzian field distribution due to aresidual iron impurity, which is known to exist in the present samples. Considering these, we used the following
12. 実験方法及び結果（つづき） Experimental method and results (continued)
form for the curve-fit analysis of the ZF-µSR time spectra: A(t) =A(t)0.10

Ag sample holder. Figure 2 shows the temperature dependence of the0.08

magnetically ordered volume fraction (MVF) in x = 0.54 deduced

0.06

from the A0, where the magnetic phase emerges below ~100 K, and0.04

gradually develops with decreasing temperature. MVF becomes

0.14

mostly independent of temperature below ~50 K to reach 0.84(2) at
A(t)0.62, 0.66, respectively. Thus, it is revealed that TN in x > 0.5 is

0.10
0.08

0.04

revealed by our previous experiment (proposal No. 2014AUD101).

0.18

To investigate the more detailed property of the magnetism, weA(t)

0.12
0.10

It is revealed that rotating frequency at the lowest temperature [58(1)0.08MHz] has much increased compared to that of x = 0.45 in La1111-H

0.06
0.04

[5.13(7) MHz], indicating that the magnetic structure of Fe atoms

almost identical to that in La1111-H with x ≥ 0.45. Additionally, we

x = 0.54
125 K
100 K
85 K
5K

0.14

setup at PSI, Swiss with x = 0.44 (non-superconducting sample). We

at the lowest temperature with x > 0.44 are almost unity, which is(c)0.16

performed additional µSR experiment using high-time resolution

maybe different from one another. Magnetic volume fraction (MVF)x = 0.62
150 K
110 K
85 K
5K0.06slightly lower than that in LaFeAsO1-xHx (La1111-H) with x > 0.5, asobserved the fast relaxation and oscillation of the signal below 80 K.

(b)

0.12

the lowest temperature. We determined the onset of TN = 98(5) K bylinear extrapolation, in the same manner, 100(8) K, 95(2) K, with x =x = 0.66
130 K
100 K82 K5K

0.12

phase, A0 is a initial asymmetry for sample volume, and ABG is atemperature independent background coming from muons stopped at(a)0.14

A0exp(-λt) + ABG, where λ is the relaxation rate of the non-magnetic

0246Time (µs)

810Figure 1: ZF-µSR time spectra for x =0.66 (a), 0.62 (b), and 0,54 (c).

= 0.62. Although this behavior is also analogous to La1111-H,
maximum of the TN ~100 K is slightly lower than that of La1111-H(~120 K).
It is known that substitution of Ce for La brings in a chemicalpressure to the system, resulting the decrease of the As-Fe-As bondangle α and the increase of pnictogen height (hAs). Since both are key
parameters for the Fermi surface as pointed out by theoretical works,

Magnetic Volume Fraction

found that x dependence of the TN seems to have a maximum around x
1.0

CeFeAsO1-xHxx = 0.54

0.8
0.6
0.4
0.2
0.00

information on crystal structure in low-temperature phase is importantfor better understanding of the magnetism in this system. To achieve

Figure2:100
200
Temperature (K)300

Fractionalofyieldmagnetic phase in x = 0.54.

this, further investigation is currently in progress.
In summery, µSR experiment on Ce1111-H with x ≥ 0.44 reveals theexistence of magnetic phase. There are difference of the magnetic properties between Ce1111-H and La1111-H,
which may originate from the magnitude of the chemical pressure.
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