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

2014A0224

Yasuhiro Miyake

実験課題名 Title of experimentSR study of BEDT-TTF-based organic antiferromagnets with 'phase under high pressure
実験責任者名 Name of principal investigator

装置名 Name of Instrument/（BL No.）

Kazuhiko Satoh2014/5/25-2014/5/28

D1
実施日 Date of Experiment

所属 Affiliation
Graduate School of Science and Engineering, Saitama 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.
'-(BEDT-TTF)2ICl2

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.

Organic compound ’-(BEDT-TTF)2ICl2 shows antiferromagnetic transition at 22 K under ambient pressureand precession SR signal is observed below Neel temperature, TN. This compound becomes superconductor
under ultra-high pressure around 8 GPa. Antiferromagnetic correlation is considered to play important role forsuperconductivity of ’-(BEDT-TTF)2ICl2 and microscopic study of magnetic state under high pressure isdesired. We have carried out preliminary SR measurement ’-(BEDT-TTF)2ICl2 under high pressure at
TRIUMF and found that both Nèel temperature and spontaneous precession frequency in the antiferromagnetic
state are strongly enhanced at 1.8 GPa. Below 0.7 GPa, however, amplitude of precession signal becomes small
and we cannot detect precession signal. As one hole is injected to (BEDT-TTF)2 dimer, spin of dimer isconsidered to be 1/2 and magnitude of spin will be same in high pressure. Enhancement of precession
frequency above 0.7 GPa and absence of high precession component below 0.7 GPa suggest thatpressure-induced magnetic phase transition occurs around 0.7 GPa and volume fraction of high-pressure
magnetic phase increases with pressure. In order to confirm this suggestion, precise high pressure SRmeasurement using new high pressure cell is desired.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
We carried out high-pressure SR experiment for organic antiferromagnet '-(BEDT-TTF)2ICl2
using newly designed high pressure cell which has relatively high signal-to-noise ratio in order toinvestigate the influence of pressure on the magnetic state. Applied load is 3.3 ton andcorresponding pressure is estimated to be about 0.7 GPa at room temperature. It should be notedthat pressure is somewhat reduced at low temperatures due to contraction of pressure medium.
Figure 1 shows zero-field SR signal of ’-(BEDT-TTF)2ICl2 around Neel temperature. Since SRsignal of ’-(BEDT-TTF)2ICl2 above Neel temperature is temperature-independent and SR signal
begin to change below 26.9 K, Neel temperature increases to about 27-28 K. Previous results about
pressure dependence of Neel temperature suggests that pressure of present work is about 0.4 GPa.
Figure 2 shows zero-field SR signal under 3.3 ton of ’-(BEDT-TTF)2ICl2 at 60.9 K (normal state)
and 7.4 K (antiferromagnetic state), respectively. Precession SR signal from ’-(BEDT-TTF)2ICl2
can be observed in the antiferromagnetic state and new high-pressure cell is found to be useful for
low density materials such as organic systems. Precession frequency at 7.4 K is 0.17 MHz which isalmost the same as the ambient pressure value. Since the precession frequency is enhanced to 1
MHz above 0.7 GPa, some significant change, e. g. pressure-induced magnetic phase transition, isexpected between 0.4 and 0.7 GPa and further study is desired.

Fig. 1 SR spectrum for '-ET2ICl2 aroundFig. 2 SR spectrum for '-ET2ICl2 in thethe Neel temperature.

normal and antiferromagnetic state.

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