SciPost Phys. Proc. 11, 002 (2023)

Single crystal growth of PrNiGe2 compounds
Kousei Ishiwatari1 , Kaito Hoshii1 , Keisuke Ida1 and Masashi Ohashi2⋆
1 Graduate School of Natural Science and Technology, Kanazawa University,Kakuma-machi, Kanazawa 920-1192, Japan
2 Institute of Science and Engineering, Kanazawa University,Kakuma-machi, Kanazawa 920-1192, Japan⋆ ohashi@se.kanazawa-u.ac.jp
International Conference on Strongly Correlated Electron Systems(SCES 2022)
Amsterdam, 24-29 July 2022
doi:10.21468/SciPostPhysProc.11

Abstract
We report on the magnetic characterization of a praseodym intermetallic PrNiGe2 . Several single crystals are grown by the Czochralski method from Ni- deficient sample as
the initial one. X-ray analysis of PrNi0.8 Ge2 indicated the CeNiSi2 -type structure as theonly phase. The magnetic measurements clearly indicate that PrNi x Ge2 exhibits a ferromagnetic orderings at 12 K, which is independent with of composition of Ni. A strong
anisotropy along the three principal crystallographic directions was observed, reflecting
the orthorhombic symmetry of the crystal structure. The b-axis was found to be the easy
axis of magnetization.
Copyright K. Ishiwatari et al.
This work is licensed under the Creative Commons
Attribution 4.0 International License.
Published by the SciPost Foundation.

1

Received 15-08-2022
Accepted 10-05-2023
Check forupdates
Published 05-06-2023
doi:10.21468/SciPostPhysProc.11.002

Introduction

The ternary compounds CeTX2 (T = transition metal and X = Si, Ge, Sn) form a large family
having the orthorhombic CeNiSi2 -type layered structure, which is constructed from deformed
fragments of the CeGa2 Al2 and α-ThSi2 structures [1–3]. The lattice parameter along b-axis
is extremely large compared to those along a- and c- axes, and it is expected that highly
anisotropic magnetic property exists. Indeed, these compounds have received considerable
interest of a great variety of magnetic behaviors [4–6]. There are not so many reports on single
crystal growth due to the difficulty in obtaining single phase samples. On the other hand, themagnetic properties of polycrystals of RT x Ge2 (T: Fe, Co, Ni, Cu, x < 1) have been investigatedin a previous study, and it seems to be easier to grow polycrystals when the amount of T is
reduced [7–10]. PrNiGe2 is known to order ferromagnetically below 13 K [11]. In this study,
we have grown a single crystal of PrNi x Ge2 and report the anisotropic magnetic properties
here.
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SciPost Phys. Proc. 11, 002 (2023)

Figure 1: Photograph of a single crystal ingot of PrNi0.8 Ge2 .

2

Experimental

The polycrystalline samples of PrNi x Ge2 (x = 0.6, 0.8, and 1.0) were prepared as starting
materials by arc-melting praseodym (99.9% ), nickel (99.99% ) and germanium (99.999% )in a tetra-arc furnace under argon atmosphere. To improve homogenity, the ingot was turned
over and remelted several times. The weight loss is negligible. Single crystals were grown by
a Czochralski pulling method. The pulling parameter was kept constant during the growth(pulling rate: 10 mm/h; seed rotation speed: 10 rpm; crucible-rotation speed: 5 rpm). An
ingot was 2-3 mm in diameter and 30 mm in length as shown in Figure 1. Its homogeneity andchemical composition were checked by microprobe analysis, which was made using JEOL SEM
and Oxford Instrument EDX at Venture Business Laboratory Kanazawa University, based on themeasurement of the Ce Lα1 , Ni Kα1 and Ge Kα1 X-ray emission lines. The experimental atomic
percentages of PrNi x Ge2 are obtained to be Pr 25.3%, Ni 23.7% and Ge 50.9% for x = 1.0,Pr 30.0%, Ni 26.6% and Ge 43.3% for x = 0.8, and Pr 21.5%, Ni 16.4% and Ge 61.9%
for x = 0.6, respectively.
The samples were checked by conventional x-ray powder diffraction experiments usingCu-Kα radiation. The single crystalline state was confirmed using back-scattering Laue technique. The dc magnetic susceptibility was measured in the temperature range 2.0-300 K using a Quantum Design MPMS-5 superconducting quantum interference device magnetometer.
The specific heat was measured by utilizing the Heat Capacity option on a Physical Properties
Measurement System.

3Results and Discussion

Figure 2 shows X-ray powder diffraction pattern of PrNi x Ge2 . All diffraction peaks can beindexed in the orthorhombic CeNiSi2 type layered structure (space group Cmcm), as shown inthe calculated spectrum. The lattice parameters a, b, and c are determined by a least-squares
approximation from the d-values corresponding to the reflections, and are gathered in Table 1.
They are consistent with those of previous reports [7, 11].
The specific heat of PrNi x Ge2 single crystal is shown in Figure 3. All samples show ananomaly reaching a maximum of ∼14 J mol−1 K−1 at 12 K. It is consistent with the previous
result of PrNiGe2 polycrystalline sample [11], which is associated with the onset of ferromagnetic order. A small anomaly is observed only in PrNi0.6 Ge2 at ∼17 K, indicating some magnetic
impurity may be included because the sample deviate from stoichiometry.
Figure 4 shows the temperature dependence of M /H in a magnetic field of 1 kOe and the002.2

SciPost Phys. Proc. 11, 002 (2023)

Figure 2: The X-ray powder diffraction pattern of PrNi x Ge2 . Indices are shown forthe peaks of the calculated spectrum.
Table 1: Lattice parameters in the orthorhombic structure of XRD patterns and theunit cell volume of PrNi x Ge2 .
x1.0
0.80.6

a (Å)
4.235
4.237
4.267

b (Å)
16.80
16.78
16.77

c (Å)
4.212
4.191
4.201

V (Å3 )
299.7
298.0
300.6

inverse magnetic susceptibility of PrNi x Ge2 . A strong decrease in magnetization is observedat around 13 K for both x=1.0 and 0.8 samples, which is consistent with the result of specificheat measurement. The magnetic susceptibilities of those compounds in the paramagnetic
state are fitted using the following formula:
M /H(T ) =N µ2eff
3kB (T − Θ)

+ χ0 ,(1)where N is the Avogadro number, kB is Boltzmann’s constant, Θ is the paramagnetic Curie temperature, and χ0 is a temperature-independent part of the magnetism including the diamagnetic core correction, the Pauli susceptibility of the electron gas, or the Van Vleck temperature
independent paramagnetism.
Fitting was carried out in the temperature range
100 K < T < 180 K. Θ, χ0 , and the effective magnetic moment µeff are given in Table 2.
The χ0 values are relatively large for both x=1.0 and 0.8 compounds while the µeff values arein good agreement with the Hund’s rule ground state for Pr3+ ion (3.58 µB ).
Table 2: Magnetic data for PrNi x Ge2 compounds.

Θ (K)µ r me f f (µB )χ0 (10−3 emu/mol)
M [5T, 5K] (µB )PrNiGe2b-axis
46.1
3.47
1.93
2.55

PrNi0.8 Ge2
a-axis
−6.1
3.06
1.63
0.679

PrNi0.8 Ge2
b-axis
48
3.34
1.88
2.89

PrNi0.8 Ge2
c-axis
−6.0
2.99
1.78
0.982

The isothermal magnetization of PrNi x Ge2 measured at T = 5.0 K along the three principal
crystallographic directions is shown in figure 5 (a). For H//b-axis the magnetization increases
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SciPost Phys. Proc. 11, 002 (2023)

Figure 3: The specific heat of PrNi x Ge2 .

Figure 4: (a) M /H and (b) the inverse magnetic susceptibility as a function of temperature in a magnetic field of 1 kOe along b−axis of PrNi x Ge2 .
more rapidly with field than along the other two directions, thus indicating the b-axis as theeasy axis of magnetization. Hysteretic behaviour is observed especially along b-axis, confirming the ferromagnetic ground state. At 5.0 K the magnetization saturates to 2.55 µB /Pr and2.89 µB /Pr for PrNiGe2 and PrNi0.8 Ge2 , respectively, which is larger than that of a PrNiGe2
porycrystalline sample [12]. The saturation moment of the free Pr3+ ion (gJ JµB = 3.20µB ) isrelatively close to the saturation magnetization of PrNi0.8 Ge2 .
Figure 5 (b) show the temperature dependences of the inverse magnetic susceptibility ofPrNi0.8 Ge2 . The anisotropy in the magnetic susceptibility along the three principal directions
is clearly evident. The magnetic susceptibilities in the paramagnetic state are fitted using theformula (1). Fitting was carried out in the temperature range 100 K < T < 180 K. The Weisstemperature Θ is positive for b-axis, as expected for a ferromagnetic ordering compound. On
the other hand, Θ is negative for a- and c-axes.

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SciPost Phys. Proc. 11, 002 (2023)

Figure 5: (a) The inverse magnetic susceptibility as a function of temperature (b)The field dependence of the magnetization of PrNi0.8 Ge2 at 5.0 K in a magnetic fieldof 1 along a-, b-, and c-axes of PrNi0.8 Ge2 .

4SummaryIn this study PrNiGe2 single crystals are grown by the Czochralski method from Ni- deficient
sample as the initial one. X-ray analysis of the sample indicated the CeNiSi2 -type structure
as the only phase. The specific heat and the magnetic measurements clearly indicate thatPrNi x Ge2 exhibits a ferromagnetic orderings at 12 K, which is independent with of compositionof Ni. A strong anisotropy along the three principal crystallographic directions was observed,
reflecting the orthorhombic symmetry of the crystal structure. The b-axis was found to be theeasy axis of magnetization. From the result of the magnetic susceptibility along the b- plane,
the effective magnetic moment is close to the value expected for the free Pr3+ ions, while atemperature-independent part of the magnetism remains.

Acknowledgements
This work was financially supported by Takahashi industrial and economic research foundation, Shibuya science culture and sports foundation, and Yamada science foundation.

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