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. 2014B0289

装置責任者 Name of responsible person

実験課題名 Title of experiment

Kenichi Oikawa

Magnetic Field and Time Dependent Magnetic Structures in Frustrated

装置名 Name of Instrument/（BL No.）

Antiferromagnets

BL10

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Hiroyuki Nojiri

2015.3.3-3.12

所属 Affiliation
Institute for Materials Research, Tohoku University
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.

LuFe2O4 single crystal

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.
This proposal is to investigate the time dependent magnetic structures in the frustrated antiferromagnets under
the stimulus of pulsed magnetic fields. The proposal has two steps, (1)time dependence of magnetic structure in
LuFe2O4 in the giant hysteresis loop and the remnant state, (2) magnetic structure switching at themetamagnetic transition in LiNiPO4. In the present run, we could only conducted the subject (1) because of thebeam time changes.
LuFe2O4 shows a ferrimagnetic ordering below room temperature and this transition is associated with a chargeordering of trivalent and divalent Fe ions as shown in Fig. 1. As shown in Fig. 2, a giant hysteresis is observed inmagnetization process at low temperatures. On the other hand, the charge and the magnetic ordering become
diffusive in lower temperatures. The relation between these two unusual behaviors has not been clarified yet.
Figure 3 shows the comparison between the initial and the magnetized states. The TOF spectra are taken at zero
fields. It is found that the intensity of magnetic [1/3 1/3 0] peak decreases in magnetized state. There is nochange in the nuclear [1 1 0] peak. In the present scattering condition, the magnetic field is applied along thec-axis and the magnetic moments are also along c-axis. In this case, domain distribution does not affect to theintensity of [1/3 1/3 0] peak because there is no magnetic moment along the scattering vector.
The present results means that the magnetic correlation becomes weaker in the magnetized state. This finding
contradicts with the simple expectation that the magnetic correlation is enhanced when the system is in fully
magnetized ferromagnetic state. It should be noted that there is no broadening of magnetic Bragg peak, whichrules out the lowering of dimensionality.
12. 実験方法及び結果（つづき） Experimental method and results (continued)

Fig. 1 Magnetic structure of LuFe2O4. Double
hexagonal layers are consists of Fe3+ and Fe2+ richlayers with ferrimagnetic ordering.

Fig. 2 Temperature dependence of magnetization curve
withgianthysteresis
andlargeremnantmagnetization.(Phys. Rev. Lett. 101(2008)137203).

Figure 4 shows the diffraction pattern in the magnetic field of 20 T. The magnetic field applied to [1/3 1/3 0] peakand not for [1 1 0] peak. Although the statistic is very low, we can see the clear reduction of [1/3 1/3 0] peak in 20 T
magnetic fields. The small shift of the peak position is also found for [1 1 0] peak. This shift is absent in the TOF
spectrum of Fig. 3. The difference of these two states is in the number of applied magnetic field pulses. Namely, by
the repetition of the magnetic field application, the change of nuclear [ 1 1 0] is introduced. To understand the originof this behavior, we are conducting the detailed analysis.

Fig. 3 TOF Spectrum at B=0 for initial ZFC andmagnetized states.

Fig. 4 TOF Spectrum in 20 T.

In summary, we have observed the large reduction of magnetic Bragg peak intensity after the single shot pulsed
field．On the other hand, there is no change of the Bragg peak profile. When the magnetic field application isrepeated, change of [1 1 0] peak is observed. The magnetic Bragg peak at 20 T is much reduced in intensity.

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