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

課題番号 Project No.

装置責任者 Name of responsible person

2016B0070

Nakajima, Kenji

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Anomalous excitations study of spin frustrated RBaFe4O7 (R=Yb, Lu)

BL14 AMATERAS

system

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2016/Dec./07-2016/Dec./13

KAMAZAWA, Kazuya
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. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.

RBaFe4O7 (R=Yb, Lu) polycrystalline samples

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.

Based on our previous neutron scattering studies of YBaFe4O7-δ and HoBaFe4O7, in order to verify ourhypothesis, that is spin dynamic becomes very fluctuate when the rare earth ion R is nonmagnetic while the spin
dynamic becomes rather static when the magnetic moment of R is large, we have carried out another neutron
scattering measurements of YbBaFe4O7 and LuBaFe4O7. We used multi-incident neutron energies with Ei of30.27, 11.60, and 6.077 meV in the measurements.

From the elastic profiles around ω ~ 0 meV, any additional

Bragg peak and peak broadening are not observed in all temperature (T) for both YnBaFe4O7 and LuBaFe4O7.
Therefore, there is no structural and magnetic transition, and they keep cubic symmetry to the lowest T that wemeasured. In inelastic scattering region, a streak scattering which is seen in YBaFe4O7 was observed in both
LuBaFe4O7 and YbBaFe4O7. (Fig. 1(a)(b)) We can confirm reproducibility for the streak scattering in
non-magnetic R ion system. Therefore we can emphasize that the streak scattering is not a fake signal but a real
signal. It is interesting that even in YbBaFe4O7, we can see almost the same intensity of the streak scattering(although we can not identify why the intensity at around 10 meV becomes weak in the streak). The
similar spin dynamics which keeps antiferromagnetic hexagon spin cluster correlation is realized in YbBaFe4O7.
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2. 実験方法及び結果（つづき） Experimental method and results (continued)
InYbBaFe4O7of4K,

thestrongdispersionless excitation is observed at ω =1 meV, and it originates from the YBO6
crystal field excitation (Fig. 2(a)). At 10 K,
the ω = 1 meV excitation disappear and anotherdispersionless excitation is observed at 0.5 meV.
Although there are back ground signals from3He cryostat which can be identified with thedata of LuBaFe4O7, the 0.5meV excitation is toostrong to identify as the background. It is a real
single indicating a phase transition relating withYbO6 crystal field (Fig. 2(c)). For the ω = 18
meV excitation, since it is not observed inLuBaFe4O7, it is considered to be intrinsic signalof YbBaFe4O7. At least it does not originate
from YbO6 crystal field excitation, but the origin
is not identified yet. In summary, spin dynamics

Fig.1 I(Q, ω) map of YbBaFe4O7 at 4 K (a), LuBaFe4O7 at 2.7K (b).
(c). Positive side of energy spectra sliced at 1<|Q|<1.5A-1. Here alldata are obtained by incident energy Ei = 30.27 meV. (d) Crystal
structure of Yb,LuBaFe4O7. Green sticks indicate a hexagon cluster.

of YbBaFe4O7 is rather similar to that ofYBaFe4O7 and LuBaFe4O7 than that of HoBaFe4O7. Then our expected state that has spin dynamic in between
R’=Ho and Y seemed to be realized. In case of R’=Ho, spin dynamics of Fe ions is madeweaken by adhesive

force due to large Ho magnetic moment, that is, spin fluctuation originated from frustration effect becomes morestatic and dynamical Jahn-Teller effect appears.

On the other hand, in case of R’=Yb as we predicted that themoment of Yb is small, the adhesive force is smaller and the similar effect did not realize. This is consistent withthe results of the magnetic susceptibility that the effective magnetic moment of HoBaFe4O7 is observed verysmaller than that weexpected, but thatof YbBaFe4O7 isobserved

almostfull value.
The data analysis
still continues forpublication.
Fig.2 I(Q, ω) map of YbBaFe4O7 at 4 K(a), YbBaFe4O7 at 10K (b), andLuBaFe4O7 at 2.7 K (c). Temperaturedependences of energy spectra ofYbBaFe4O7 (d - left) and LuBaFe4O7 (d right), which are obtained from sliced I(Q,ω) map with 1 < |Q| < 2 A-1 region. Here,all data are obtained by incident energy Ei= 6.08 meV.

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