実験報告書様式（一般利用課題・成果公開利用）

MLF	 Experimental Report

提出日 Date of Report2015.12.10

課題番号 Project No.

装置責任者 Name of responsible person

2015A0060

Shin-ichi Itoh

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Magnetic excitations in heavy-electron ferromagnets NdT4P12 (THRC (BL12)= Fe and Ru)

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2015.10.28 – 2015.11.5

Kazuaki Iwasa
所属 Affiliation
Department of Physics, Tohoku 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.
NdFe4P12 single crystal
NdRu4P12 powder

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.

Rare-earth filled skutterudite compounds, NdFe4P12 (L. Keller et al., J. Alloys and Comp. 323–324, 516(2001)) and NdRu4P12 (H. Sugawara and C. Sekine, private communication, S. Masaki et al., PRB 78, 094414(2008)) exhibit ferromagnetic ordering at 1.9 and 1.6 K, respectively. In addition, the electrical resistivity dataof NdFe4P12 show an increment with decreasing temperature below approximately 20 K (H. Sato et al., PRB 62,15125 (2000)). This behavior is considered to be caused by the Kondo effect because the observed
phenomenon of resistivity is reproduced by a function of temperature, –logT. On the other hand, a lesssignificant anomaly in the resistivity was found for NdRu4P12 (T. Utsumi et al., Muroran Inst. Tech. Journal 49,93 (1999) (in Japanese)). In order to investigate electronic correlation owing to hybridization between
rare-earth 4f electrons and conduction electrons in these compounds, we performed inelastic neutron
scattering (INS) experiments to identify magnetic excitation spectra at low-temperature region. As described
below, we observed magnetic excitation spectra for both compounds. In addition, we attempt to measure INS
spectra below 1 K by using the 3He closed-cycle refrigerator and the oscillating collimator, which are installed
to HRC (BL12).
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2. 実験方法及び結果（つづき） Experimental method and results (continued)
Single crystalline sample of NdFe4P12 and that ofpolycrystalline sample of NdRu4P12 were synthesized by theSn-flux method. The INS measurement for NdFe4P12 wascarried out using the 3He closed-cycle refrigerator, which
was rotated by a goniometer, and the oscillating collimator.
For the measurement for NdRu4P12, the GM cryostat wasused without the oscillating collimator.
Figure 1 shows a measured INS spectrum of NdFe4P12(open squares), together with background data for an empty
sample cell (open triangles). Close circles are results ofsubtraction of the background data from the sample data,
which give an actual excitation spectrum of NdFe4P12. A
horizontal bar located between 20-27 meV indicates the
instrumentalresolution.

The

excitation

spectrumisremarkably broader than the resolution.

Fig. 1. INS spectra of NdFe4P12. Squares andtriangles are data of the sample run and theempty-cell run, respectively. The difference
shown by filled circles corresponds to theexcitation in NdFe4P12. A horizontal bar
located at 20-27 meV indicates theinstrumental resolution width (FWHM) for Ei= 92.16 meV.

Figure 2 shows a result of INS measurement for NdRu4P12.
Although we had no time to measure background data, we
identified a sharp peak located at 27 meV, whose spectral
width is almost the same as that of the resolution. We also
detected a peak at 152 meV (not shown here). These two
peaks can be attributed to excitations between three
crystalline-electric-field (CEF) levels, which appear under
the cubic point group at the Nd-ion site of this compound.
Intensity above 30 meV seen in Fig. 2 does not depend on
temperature, so that this is not ascribed to excitations of thesample.
The same excitation could be expected also for NdFe4P12.
Therefore, the broadening of INS spectrum of NdFe4P12 issuggestive of coupling of the 4f electrons with other degrees

Fig. 2. INS spectra of NdRu4P12. Circles andtriangles are data measured at 3 and 280 K,
respectively. A horizontal bar located at20-31 meV indicates the instrumental
resolution width (FWHM) for Ei = 205.9 meV.

of freedom. As for the heavy-fermion system, hybridization
between the 4f and conduction electrons is a candidate explanation to the spectral broadening. However, themomentum-transfer dependence of the INS intensity is not simply reproduced by the magnetic form factor of
Nd3+ ion state. Another mechanism for the spectral broadening is coupling between the CEF excitation and thephonon modes.
In order to investing further the effect of phonon mode on the CEF excitation as well as the ferromagnetic
heavy-electron behavior, it is necessary to measure temperature dependence of the broad spectrum.

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