実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report

課題番号 Project No.

装置責任者 Name of responsible person

2016B0055

Toru Ishigaki

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Magnetic structure of new structure Fe based superconductor BL20, iMATERIA
EuRbFe4As4

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2017/3/31 – 2017/4/1

Kazuki Iida所属 Affiliation
CROSS Tokai
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. Pleaseadd figures and tables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.

Polycrystalline EuRbFe4As4.

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.
Recently, new-structure-type iron-based superconducting materials AeAFe4As4 (Ae = Ca, Sr, Eu and A =K, Rb, Cs) were reported, one of which is EuRbFe4As4. EuRbFe4As4 shows bulk superconductivity below Tc =36.5 K. BaFe2As2 is a non-superconducting parent material with antiferromagnetic transition at TN = 143 K, andupon K+ substitution at Ba2+ site, (Ba0.5K0.5)Fe2As2 shows superconductivity below Tc ~ 38 K. Similar toBaFe2As2, EuFe2As2 is also a non-superconducting parent material with antiferromagnetic transition at TN =190 K. As in (Ba0.5K0.5)Fe2As2, Rb+ substitution at Eu2+ site in EuFe2As2 gives rise to hole doping, resulting insuperconductivity in EuRbFe4As4. Furthermore, Eu sublattice in EuRbFe4As4 shows ferromagnetic order below
15 K. However, no detailed diffraction measurement has been performed on EuRbFe 4As4. Therefore, themagnetic structure as well as microscopic measurement on possible interplay between superconductivity andferromagnetism in EuRbFe4As4 was investigated using iMATERIA.
Polycrystalline EuRbFe4As4 was put into the annular type Vanadium cell whose outer and inner radii are 10and 9 mm. The cell was attached to the GM refrigerator, and measurements were performed at 4 and 20 K.

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2. 実験方法及び結果（つづき） Experimental method and results (continued)
Single frame mode was used and the data shown here is obtained by the LA15 bank. All index shown thisreport are described assuming the P4/mmm symmetry.
Figure 1 shows the neutron diffraction patterns from EuRbFe4As4 below and above TC (4 and 20 K). Below

TC, the magnetic Bragg peaks of (100) at Q = 1.62 Å-1 was observed. Since weak nuclear Bragg peak also
exist at (100), observed magnetic peak is consistent with the ferromagnetic structure indicated by the bulk
measurements. On the other hand, the clear magnetic peak is also observed at Q = 0.52Å-1 at 3.7 K. Since Q= 0.52Å-1 correspond to (0.224 0.224 0), (0.317 0 0), or (0 0 0.111), either of which is incommensurate. Thus,
the magnetic structure of EuRbFe4As4 is not simple ferromagnetic structure. Since the current sample is thestrong absorber of neutrons, we are doing careful analysis to obtain the magnetic structure.
Finally, we would like to appreciate the iMATERIA team for their help.

Figure 1. Neutron powder diffraction patterns from EuRbFe4As4 at 3.7 and 20 K using the LA15 bank ofiMATERIA. Positions of nuclear Bragg peaks are also shown.

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