Photon Factory Activity Report 2018 #36 (2019)

BL-8A/2016G143

X-ray diffraction experiments in quadrupolar Kondo candidate PrTi2Al20 and PrV2Al20Daisuke Okuyama1, Masaki Tsujimoto2, Hajime Sagayama3, Yasuyuki Shimura2, Akito Sakai2,
Atsushi Magata2, Satoru Nakatsuji2, and Taku J. Sato1
1
IMRAM, Tohoku University, Sendai 980-8577, Japan
2
ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
3
CMRC and PF, IMSS, KEK, Tsukuba, Ibaraki 305-0801, Japan
Crystal structure analyses in PrTr2Al20 (Tr = Ti and V) has been carried out. We found that Pr-Al cage for PrV2Al20 is
anisotropically deformed from sphere, which modify the crystalline-electric-field levels of Pr3+. The information would
provide a clue to understand the anomalous properties in PrTr2Al20.

1 Introduction
Non-magnetic PrTr2X20 (Tr = transition metal, X = Aland Zn) compounds have been extensively studied as
candidates for the two channel (quadrupolar) Kondo
effect. In PrV2Al20, magnetic susceptibility and electric
resistivity show anomalous T1/2 behavior at low
temperatures, which is in good accordance with thetheoretical prediction for the two channel Anderson
lattice model [1]. In stark contrast, PrTi2Al20 shows T2behavior below ∼ 20 K. They show quite different
ordering behavior. PrTi2Al20 shows ferro-quadrupolarorder at T ∼ 2 K [2]. In contrast, PrV2Al20 shows
successive non-magnetic anomalies at much lower
temperatures around 0.6 K, of which the origin issuggested to be antiferro-quadrupolar type [3]. The
crystal-electric-field (CEF) levels of Pr3+ in PrTi2Al20
were determined as Γ3 (quadrupolar- and octapolar-active
ground state) - Γ4 (5.61) - Γ5 (9.30) - Γ1 (13.5 meV),whereas it was not explored in PrV2Al20 [2]. The detailed
knowledge on the crystal structures would provide a clue
to understand the difference of the anomalous transport
behavior. Thus, we reinvestigated crystal structure
analysis of the PrTr2Al20.
2 Experiment
X-ray diffraction experiments were performed using
single crystals with diameters of about 30 µm on the BL8A. The photon energy of the incident X-rays was tuned
at 18 keV. X-ray beams were shaped into a square of 200x 200 µm2 by a collimator. The intensity data wereconverted to the |F|-tables by using Rapid- Auto program,Rigaku. We used CrystalStructure program of Rigaku foranalyzing the crystal structure from the |F|-table.
3 Results and Discussion
The crystal structure analyses for single crystals ofPrTi2Al20 and PrV2Al20 were performed.
The
comparisons between observed and calculated structure
factors are shown in Fig. 1(a). The crystal structure
consists of two Al-cages with individually capturing Prand Tr atoms as shown in Fig. 1(b). The CEF x and W
parameters were known as x s= 0.25(1) and W = -1.53(3)K for PrTi2Al20 [2]. Using the point charge calculation
based on the refined structural parameters of Tr = Ti, weestimated the Al-charges that are consistent with the x andW parameters. The estimated Al-charges are +0.9 forAl(1) and +0.88 for Al(3). Next, we assumed that Alcharges estimated at Tr = Ti are also applied to Tr = V,
and obtained x ∼ 0.41 and W ∼ -2.1 K using the pointcharge model based on the refined structural parameters
for Tr = V. By these parameters, the CEF excited levels
can be estimated as Γ4 ∼ 5.6, Γ5 ∼ 11.1, and Γ1 ∼ 13.5
meV for PrV2Al20. Detailed information is found in [4].

Fig. 1: (a) Observed (Fobs) and calculated (Fcal) structure
factors for PrTr2Al20 (Tr = Ti and V). (b) Schematic of
crystal structure of PrTr2Al20.
References[1] A. Sakai and S. Nakatsuji, J. Phys. Soc. Jpn. 80,063701 (2011).
[2] T. J. Sato, S. Ibuka, Y. Nambu, T. Yamazaki, T. Hong,
A. Sakai, and S. Nakatsuji, Phys. Rev. B 86, 184419(2012).
[3] Y. Nakanishi, M. Taniguchi, M. M. Nakamura, J.
Hasegawa, R. Ohyama, M. Nakamura, M. Yoshizawa, M.
Tsujimoto, S. Nakatsuji, Physica B 536 125 (2018).
[4] D. Okuyama et al., J. Phys. Soc. Jpn. 88, 015001(2019). *okudaisu@tohoku.ac.jp