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

2017A0005

Ryoichi Kajimoto

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Magnetic excitations in the new-structure Fe-based

4SEASONS (BL01)

superconducting material EuRbFe4As4

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2017/4/28 – 2017/5/2

Kazuki Iida所属 Affiliation
CROSS
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.
Polycrystalline EuRbFe4As4 (approximately 4 g).

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.

Very 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 withantiferromagnetic transition at TN = 143 K, and upon K+ substitution at Ba2+ site, (Ba0.5K0.5)Fe2As2shows superconductivity below Tc ~ 38 K. Similar to BaFe2As2, EuFe2As2 is also anon-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 TC = 15 K. However, no inelastic neutron scattering measurement has been performed on
EuRbFe4As4. Therefore, the neutron resonance and ferromagnetic spin wave excitation as well asinterplay between superconductivity and ferromagnetism in EuRbFe4As4 has been investigated using
4SEASONS.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
About 3.94 g polycrystalline EuRbFe4As4 was sealed in aluminum can whose thickness was 1 mm. Assuming
the packing factor, we estimated that the effective thickness of the sample is 0.5 mm. Given Ei = 70 meV,about half of neutrons are absorbed by the sample in the elastic channel. Time-of-flight neutron scattering
measurements were preformed using incident neutron energies of 11.3, 15.6, 22.9, 37.1, and 70.1 meV with
Fermi chopper frequency of 300 Hz. The measurements were performed at T = 10.5, 25.0, and 41.0 K. Notethat 10.5 K < TC, TC < 25 K < Tc, and 41.0 K > Tc.
To emphasize the magnetic signals, we made two different subtractions: (1) 25.0 K – 41.0 K for theneutron-resonance mode （Fig. 1) and (2) 10.5 K – 25.0 K for the spin wave excitations （Fig. 2). As seen in Fig.
1, there are magnetic resonance at Eres = 15 meV and Q ~ 1.1 Å-1 (see the red arrow in Fig. 1). Note that Eres
~ 5kBTc , which is the reasonable value for the iron-based superconductors. On the other hand, below TC, theferromagnetic spin wave excitations were observed as shown in Fig. 2. This spin wave spectrum can beunderstood by the ferromagnetic spin structure of the Eu site. Although Eu is strong neutron absorber, wehave succeeded in observing in two important features (neutron resonance mode and ferromagneticexcitation) in the new iron-based superconducting material EuRbFe4As4. We are now analyzing the data inmore detail.

Figure 1. Subtracted I(Q, ℏω) spectra (25.0 K – 41.0 K) with Ei = 37.1 meV. (b) Subtracted I(Q, ℏω) spectra(10.5 K – 25.0 K) with Ei = 11.3 meV.

2