Date of Approval 2017/07/20
Approver Takashi Ohhara
Date of Report 2017/07/19

Experimental Report
Project No.

Name of Instrument scientist

2017A0223

Takashi Ohhara
Title of experiment

Name of Instrument/ BL No.

Determination of the magnetic propagation wave vector of theBL18 (SENJU)

non-centrosymmetric heavy electron compound CePdSi3

Date of Experiment
2017/05/12-2017/05/17

Name of principal investigator
Yoichi Ikeda(5/12: setup&precooling)(5/13 13:30 ~ 5/17 9:00: on beam)Affiliation
Institute for Materials Research, Tohoku University

Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
Name of sample(s) and chemical formula, or compositions including physical form.
Sample information
Name: CePdSi3 (single crystal)
Dimension: ~ 2 mm x 2 mm x 0.05 mm-thickness
Bond: GE varnish, Holder: Cu sheet
Structural properties
Lattice constants: a = 4.331(2) Å, b = 4.331(2) Å, c = 9.61(4) Å,
90.0(2),= 90.0(2),== 90.0(3), V = 180.3(7) Å3 (which are evaluatedfrom #8101-data measured at ~0.3 K).
Crystal structure: noncentrosymmetric body centered tetragonal
Space group: I4mm (#107)
Chemical formula: Ce Pd Si3 (Z = 2)
Density: 6.094457 g cm-3, Molecular weight: 330.792 g mol-1

Fig. 1 Photograph of thesingle crystalline sample of
CePdSi3 and the Cu holder
for a 3He refrigerator.
1.4
1.2
1.0

Physical properties
Magnetic transition temperatures:

0.8

TI = 4.8 K, TII = 2.8 K, TIII = 2.3 K

0.6

Neutron scattering lengths and cross sections (cited from the NIST

0.4

data base):

0.2Atomb / fm

abs / barn

CePdSi3
H // [100]T = 2.0 K

inc / barn

At.wt. / g mol-1

Ce

4.840

0.63

0.0

140.116

Pd

5.910

6.90

0.093

106.420

Si

4.149

0.171

0.004

28.0855

Ref. [1] D. Ueta et al., JPSJ 85, 104703 (2016).

00report sample
09May2017 SENJU sample
510152025

H [kOe]Fig. 2 Magnetization curves ofCePdSi3. The sample qualityof this experiment is in good
agreement with that of thereported sample [1].

Experimental method and results.

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

[Experimental procedure]
CePdSi3 shows three successive magnetic transitions at TI = 4.8 K, TII = 2.8 K, and TIII = 2.3 K in zeromagnetic field. In order to determine the magnetic propagation vector in the three magnetic phases, we
carried out a neutron diffraction experiment with the SENJU diffractometer at BL18. To investigate themagnetic structure below TIII (phase III), we utilized a 3He refrigerator and cooled the sample down to ~0.3 K. The equator scattering plane was set into the (h0l) plane in reference to the experimental
procedure for similar noncetrosymmetric CeTSi3 systems. In this experiment, we used a radial collimatorsystem on BL18 to reduce background and spurious signals from the cryostat. The accelerator wasoperated at 150 kW, and there is no serious (long time) beam-supply stop in our experiment. From theresults of premeasurements (#8101-8104), data acquisition times were appropriately determined so that
we obtain a data set with a sufficient statistical quality. The experimental history is summarized in Fig. 3.

Fig. 3 History of our experiment at BL18. The label of I, II, and III means the phase I (TI ~ TII), II (TII ~ TIII),and III ( < TIII), respectively.
[Experimental Results]
In the paramagnetic phase (T > TI), the crystal structure of CePdSi3 was confirmed to be anoncentrosymmetric body-centered tetragonal structure (space group I4mm; #107), for which nuclear
Bragg reflections have an extinction rule of h + k + l = 2n (n: integer). For example, nuclear Braggreflections in the (1kl) plane are observed at k + l = odd, as shown in Fig. 4(a). Here the observed
nuclear Bragg reflections are indicated with blue circles. Note that (1-10), (11-2), and (1-1-2) reflectionsin Fig. 4(a) are out of the observable range for this experiment. The surveyable area in the (1kl) plane isindicated with the yellow-hatched area in Fig. 5. Lattice constants at 0.3 K were determined as a =4.331(2) Å, b = 4.331(2) Å, c = 9.61(4) Å,= 90.0(2),= 90.0(2),other parameters (position parameter z) are under analysis.

= 90.0(3), V = 180.3(7) Å3, while

Experimental method and results (continued)

Fig. 4 Neutron intensity maps of CePdSi3 on the (1kl) plane measured at (a) 5 K, (b) 3.5 K, (c) 2.5 K,and (d) 0.3 K.
Fig. 5 Surveyable reciprocal space in the (1kl) plane.
The yellow-hatched area indicates the surveyable
area for this experiment. The filled-red circles show
fundamental nuclear Bragg reflections in the (1kl)plane for I4mm space group. In this experiment,(1-10), (11-2), and (1-1-2) reflections are out ofrange.

Experimental method and results (continued)
In the magnetic phase between TI = 4.8 K and TII = 2.8 K (phase I), magnetic Bragg reflections wereobserved at several incommensurate positions described with the magnetic propagation wave vector of
1 = (0.314, 0, 0) as shown in Fig. 4(b). Here the magnetic Bragg reflections are indicated with red

circles, and the propagation vector

1 is indicated with red arrows. Note that the magnetic reflections ataround Q = (1, 1, 0) and (1, 0, -3) in Fig. 4(b) are also out of range although those reflections areequivalent with that around Q = (1, 0, -1). In the magnetic phase between TII = 2.8 K and TIII = 2.3 K(phase II), neutron intensity map is almost the same as that of the phase I, as seen in Fig. 4(c). In themagnetic phase below TIII = 2.3 K (phase III), additional magnetic reflections were observed at several
incommensurate positions described withreflections of2 = (0.686, 0, 0) as shown in Fig. 4(d), here the magnetic

2 are indicated with broken-red circles. Furthermore, significant weak satellite reflections

were observed at around nuclear Bragg positions. For example, these satellites around Q = (1, 0, -1)
are indicated with double circles in Fig. 4(d). An enlarged view around Q = (1, 0, -1) is shown in Fig.
6(left). The observed satellite peaks seems to be a 3Q-harmonics for(1,2. Additional fragile spots around0.45, -1) are under analysis.
10(1kl) plane
along [1k-1]
863Q?
for = 0.686 from (12-1)
k = -0.058(1)4III (0.3 K)
III (1.45 K)
II (2.55 K)
I (3.5 K)
PM (5 K)
3Q?
for = 0.686 from (1-2-1)
k = +0.058(1)20-0.15

-0.10

-0.05

0.00
0.05
k / r. l. u.

0.10

0.15

Fig. 6 (left) An enlarged view around Q = (1, 0, -1) in Fig. 4(d). (right) Line profiles around Q = (1, 0,-1) along the k-direction measured.

Table 1. A result of the representation analysis with "SARAh" software. Basis vectors for I4mm with 1= (0.314, 0, 0) or

2 = (0.686, 0, 0) are listed. The decomposition of the magnetic representation for

the Ce site (0, 0, 0) is

11
mag = 1 1 + 2 2 .

Experimental method and results (continued)
From a result of the representation analysis with "SARAh" software, there is two possible magnetic
structures ( 1 and2) for

1 = (0.314, 0, 0) and2 = (0.686, 0, 0) as shown in Table 1. For

moments are perpendicular to the propagation vector
structure (m // b-axis
basis

2 and

3, c2

a-axis). On the other hand,
2 + c33, so that

1, magnetic

1, indicating a transverse sinusoidal magnetic

2 is described by a linear combination of the two

2 allows the introduction of an out-of-plane (c-axis) component.

For example, for c3 = 0, magnetic moments have no c-axis component suggesting a longitudinal(sinusoidal) magnetic structure (m // a-axis). While, for non-zero c3, a longitudinal (sinusoidal) magnetic
structure with a finite out-of-plane component can be realized. The case of c2 = 0 (transverse magneticstructure; m // c-axis) may be excluded from the results of the previous magnetization measurements[1], because the c-axis of CePdSi3 is the magnetic hard axis.
A weak ferromagnetic component was observed below TII from the magnetization measurement [1], sothat the1 magnetic structure may drop out as a candidate of the magnetic structure of the phase II,and III. In this case, it is expected that neutron diffraction intensity at fundamental nuclear Bragg
positions depends on temperature. Temperature dependence of the neutron intensity is under analysis.
In conclusion, we carried out a single-crystal neutron diffraction experiment to investigate the magnetic
structure of a noncentrosymmetric compound CePdSi3 by utilizing the SENJU diffractometer at BL18,J-PARC. Clear incommensurate magnetic Bragg reflections were observed atphase I and II. In addition, additional Bragg peaks were observed at

1 = (0.314, 0, 0) in the

2 = (0.686, 0, 0) below TIII (phaseIII). From the results of the magnetization measurements and the representation analysis, we proposed
an incommensurate longitudinal sinusoidal magnetic structure ( 2: m // ac) as a possible magneticstructure in the phase I (TI = 4.8 K < T < TII = 2.8 K). The c-axis ferromagnetic component is considered
to be zero in the phase I from the results of the magnetization measurements. On the other hand, aweak ferromagnetic component was observed below TII. Therefore, an incommensurate longitudinalsinusoidal magnetic structure with a finite (uniform) c-axis component may be realized in the phase II. In
the phase III, magnetic propagation wave vector is changed to2from1.

Since two inequivalentmagnetic Bragg reflections were observed in the phase III, a phase separating state between

1 and2phases (or a weak structural transition) may occur at least at 0.3 K. Further precise analysis isindispensable for publishing.