実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report
課題番号 Project No.

提出日 Date of Report
2017/07/26
装置責任者 Name of responsible person

2017A0231

Shin-ichi ITOH
Hideki YOSHIZAWA

実験課題名 Title of experiment
Spectroscopic study on the crystalline electric field excitations
in NdB4

装置名 Name of Instrument/（BL No.）HRC (BL12)

実験責任者名 Name of principal investigator
Hiroki YAMAUCHI

実施日 Date of Experiment2017.06.19 – 06.21

所属 Affiliation
Materials Sciences Research Center, JAEA
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.
A polycrystalline powder sample of neodymium tetraborides, NdB4, was prepared by crushing single crystals.
The high-quality single crystals were grown by the floating zone method in a four-ellipsoidal mirror-type image
furnace. The sample had a total mass of 10.4 g. The 11B isotope enriched to 99.5% was used wherever possible
to keep away from the strong neutron absorption of 10B contained in natural boron. No impurity phase wasobserved by neutron powder diffraction experiments. The powdered sample was wrapped in a thin Al foil
shaped to 3 cm (height) x 2 cm (width) x 0.8 cm (thickness) and mounted inside a standard Al can with He
exchange gas. The sample can was placed inside a GM cryostat and cooled down to 3 K.

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.

Inelastic neutron scattering (INS) measurements were performed by the time-of-flight technique using thechopper spectrometer HRC (BL12) at MLF/J-PARC. The power of the accelerator was approximately 150 kW.
The rotation frequency of the Fermi chopper was 200 Hz. In the experiment, two settings for multiple incident
energies of neutrons were used mainly with Ei = 51.17 meV and 11.47 meV to target a wide range of (Q, ω)
space, and secondarily with Ei = 25.51 meV and 8.01 meV for better energy resolution. The energy resolutions

ΔE/Ei were 1.1%, 0.55%, 0.81%, and 0.44% for incident energies described above, respectively. Data werecollected at 30 K, 20 K (in the paramagnetic phase I), 9 K (in the high-temperature intermediate phase II), and 3
K (in the lowest-temperature phase IV).
The crystalline electric field (CEF) removes the ten-fold degeneracy of 4f 3 ground multiplet of Nd3+ (J = 9/2),
leading to five Kramers doublets under the tetragonal point symmetry. Figure 1 shows the INS spectra with Ei =51.17 meV. The spectra are obtained by integrating the data over the Q range of 1.5–2.5 Å-1. The low-energy
INS spectra integrated over the Q range of 0.5–1.5 Å-1 are shown in FIG. 2. At 30 K, apparent peaks areobserved approximately at 3.0 meV and 12.5 meV. As clearly seen in FIG. 3, these peaks show no dispersion
over the entire |Q| range and the intensities decrease with increasing |Q|, indicating CEF excitations (G – E1
1and G – E2).

2. 実験方法及び結果（つづき） Experimental method and results (continued)

FIG. 1. INS spectra of NdB4 with 51.17 meV incident

FIG. 2. Low-energy INS spectra of NdB4 with incident

energy neutrons at 3 K, 9 K, and 30 K.

energy Ei = 11.47 meV at 3 K, 9 K, and 30 K.

FIG. 3. Contour map of the INS intensity of NdB4 measured with Ei = 25.51 meV at 20 K.
over the entire Q range and the intensities decrease as the Q increases, indicating CEF excitations (G–E1 andG–E2). Additionally, these two excitations show peak shifts with decreasing temperature. This behavior is also
consistent with the fact that the two peaks are CEF excitations. At 9 K, new small peaks emerge around 17.5
meV and 28.5 meV without energy dispersion and increase in intensity with decreasing temperature. Thus,
they are considered to be CEF excitations (G–E3 and G–E4). In conclusion, present study succeeds to reveal theCEF level scheme of 0–3.0–12.5–17.5–27.5 [meV]. This scheme can also explain the weak traces around 14.5
meV (E1–E3) and 24.5 meV (E1–E4) at 30 K. The fact that the excitation intensities of G–E3 and G–E4 in theparamagnetic state are very weak should reflect the small mixing of the wave function components in thissystem. On the basis of this postulation and the additional fact that the excitation intensities of G–E1 and G–E2
are very strong, we calculated the tetragonal CEF parameters Blm and obtained the set of B20 = -0.87 [K], B40 =0.071 [K], B60 = -0.76 [mK], and B44 = B64 = 0 [K] that roughly explained the intensity ratio and the peak positionof the INS spectrum at 30 K. This result provides the existence of the pseudo-quartet ground state consisting of|5/2> and |7/2> with the small splitting of 3 meV, as the origin of the unusual physical properties of NdB4. In
the future, using these parameters as default, we will obtain the refined solution that can explain otherphysical quantities while taking the local symmetry of Nd3+ ions into account.
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