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
2014.07.30

課題番号 Project No.

装置責任者 Name of responsible person

2014A0184

S. Torii

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

CLARIFYING THE MYSTERIOUS INTERMEDIATE PHASE OF

BL-08

PARTIAL MAGNETIC ORDER IN CLINOATACAMITE

実施日 Date of Experiment

実験責任者名 Name of principal investigator

5/13 21:00 - 5/16 9:00

X.G. Zheng
所属 Affiliation
Saga 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.
Cu2(OD)3Cl in powder form

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.

In recent years, geometrically frustrated magnets, in which localized magnetic moments interact
through competing exchange interactions that cannot be simultaneously satisfied because of theirgeometric configuration, receive intense attention because they are playgrounds for unconventional
states such as spin liquid and other novel properties. Herbertsmithite ZnCu3(OH)6Cl2 has attracted
a lot of interest as a promising candidate to display a spin-liquid ground state on almost perfectly
decoupled two-dimensional (2D) kagome layers. Clinoatacamite, Cu2(OH)3Cl, as the parent
compound for Herbertsmithit and one of the pyrochlore lattice systems itself for the s = 1/2 AFM
Heisenberg spin, has also drawn intense attention in recent years since our report on its
unconventional phase transitions. Susceptibility and specific-heat measurements display
unexplained unconventional successive transitions at Tc1 =18.1 K and Tc2 = 6.4 K. The lowtemperature phase below Tc2 = 6.4 K is well defined by a canted Néel order, on the other hand, theintermediate phase for temperatures Tc2 < T < Tc1 still remains mysterious.
2. 実験方法及び結果（つづき） Experimental method and results (continued)1

Distinct oscillations of the muon spins with time around the baseline of 1/3, with three muon
spin precession frequencies, were observed.

Although the muon spin rotation measurements probe

the local magnetic fields at the muon stopping sites, the fact of the observed three precession
frequencies from three muon stopping sites and the baseline of 1/3 for the untextured powder
sample unambiguously demonstrated the existence of a uniform static local field, felt by the muons
throughout the whole sample, hence, it implies the development of a long-range magnetic order.
However, only a very small entropy (~0.05Rln2) was released at Tc1, and neutron diffraction
experiments found no sign of magnetic ordering. The nature of the intermediate phase is still
unknown and it is termed as a “devil compound”. Obviously further experimental and theoreticalinvestigations are demanded.

In 2014A0184 (beam time: 3 days) we had run a preliminary measurement on SuperHRPD.
We successfully observed a new magnetic reflection in the Tc2 < T < Tc1 intermediate phase (Fig.
1 below).

SuperHRPD_BS_bin4_packed16

y_int

4.75K
9K30K

3

3.1

3.2

3.3

3.4

3.5

3.63.7

3.8

d_spaceFug. 1 Preliminary results on clinoatacamite Cu2(OD)3Cl , showing new magnetic reflection ataround d = 3.32. The data have been packed 16 times to show the presence of the weak magneticpeak.

Further experiments are needed to clarify the new magnetic order.

2