Date of Report 2017/5/16
承認者 Approver Takashi Ohhara
提出日 Date of Report 2017/5/16

Experimental Report
Project No.

Name of responsible person

2017A0148

Takashi Ohhara
Title of experiment

Name of Instrument/ BL No.

Neutron diffraction study of the devil’s staircase in La5Mo4O16
Name of principal investigator

SENJU (BL18)
Date of Experiment

Ryoichi Kajimoto

2017/4/9 – 2017/4/14

Affiliation
J-PARC Center

Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1.
Name of sample(s) and chemical formula, or compositions including physical form.
Single crystal La5Mo4O16

2.
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

La5Mo4O16 consists of perovskite layers of MoO6 octahedra, where 4electrons at Mo sites in theperovskite layers have localized magnetic moments with strong Ising anisotropies, and Mo2O10 pillars connect
the perovskite layers. It is believed that Mo ions in the pillars are non-magnetic, and thus the inter-layer
magnetic interaction between the perovskite layers are expected to be very weak. In fact, La5Mo4O16
undergoes antiferromagnetic order with the magnetic propagation vector k = (0, 0, 0.5) below
1(a)], and external magnetic field along theN= 200 K [Fig.

axis (> 0.5 T) can induce the ferrimagnetic order with k = (0, 0, 0)[Fig. 1(b)]. Recently, a Waseda University group found so-called devil’s staircase in La5Mo4O16 under external
magnetic field along theaxis as shown in Fig. 1(c). To investigate in detail the nature of the magnetic devil'sstaircase by means of the single crystal neutron diffraction technique is a purpose of this experiment.
A single crystal with 40 mg was grown by the floating zone technique. We aligned the crystal in theto apply the external magnetic field along thecarried out at

axis using the “vertical 7T magnet”. Most measurements were

= 50 K, and some zero-field measurements at 4 and 220 K. Magnetic field along theapplied in the range of -5 <plane< 5 T. Data was analyzed by the software suite “STARGazer”.
1axis was

Experimental method and results (continued)

2.

Fig. 1. (a) Antiferromagnetic structure and (b) ferrimagnetic structure of La5Mo4O16. (c) Magnetization curve in
La5Mo4O16 under the external magnetic field along theaxis at 50 K.

Fig. 2. Detector maps around (-1 1 ) at 50 K under the external magnetic fields of (a) 0 and (b) 5 T. The
intensities are plotted in the log scale. Note that the Bragg peak from the other domain due to the monoclinic
structure was also observed.
Figures 2(a) and 2(b) show neutron-intensity maps under the external magnetic fields of 0 and 5 T at 50 K
using a single detector. In the absence of the external magnetic field, the magnetic Bragg peak was observed at
the AF position of (-1 1 0.5). The AF Bragg peak disappeared at 5 T, indicating that the ferromagnetic structure
is realized. On the other hand, no incommensurate magnetic peak was observed in any measured magneticfields. Instead, the intensities at the AF and ferrimagnetic peaks are changed. These results indicate that themagnetization steps such as the 1/7 plateau cannot be explained by a long-period magnetic structure.
Although further detailed analysis is required, the magnetic devil’s staircase can be explained well by thebalance of the occupancy of the AF and ferrimagnetic states, which are determined by the combination oftemperature and external magnetic fields.
Finally, we would like to appreciate the local contacts, Dr. Akiko Nakao and Dr. Taketo Moyoshi, and theMLF sample environment team.

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