Pressure dependence of the magnetic ground state in ${\mathrm{CePtSi}}_{2}$

Pressure dependence of the magnetic ground state in ${CePtSi}_{2}$

S. E. Dissanayake, F. Ye, W. Tian, M. Matsuda, H. Muto, S. Suzuki, T. Nakano, S. Watanabe, J. Gouchi, and Y. Uwatoko

Phys. Rev. B 105, 245111 – Published 9 June 2022

Abstract

${CePtSi}_{2}$ was reported to exhibit an antiferromagnetic order below $T^{*} = 1.8$ K at ambient pressure, a valence state change at $\sim 1.2$ GPa, and superconductivity in the range between 1.4 and 2.1 GPa with a maximum transition temperature of 0.14 K [T. Nakano et al., Phys. Rev. B 79, 172507 (2009)]. We have performed polycrystalline and single-crystal neutron diffraction experiments to determine the magnetic structure under ambient and high pressures. We found incommensurate magnetic peaks with a magnetic propagation vector of $(0.32, 0, 0.11)$ at ambient pressure below $T_{SDW} \sim 1.25$ K. Those magnetic peaks originate from a spin-density-wave order with the easy axis along the $c$ axis and an averaged ordered moment of $0.45 (5) μ_{B}$ , suggesting that there may be an intermediate phase between $T^{*}$ and $T_{SDW}$ . Applying pressures, the magnetic propagation vector shows no change and the magnetic order disappears around 1.0 GPa, which is much lower than the critical pressure for the superconducting phase. The results suggest that other than magnetic fluctuations may play a primary role in the superconducting pairing mechanism.

Received 22 July 2021
Revised 2 November 2021
Accepted 26 May 2022

DOI:https://doi.org/10.1103/PhysRevB.105.245111

Physics Subject Headings (PhySH)

Antiferromagnetism Superconductivity

Heavy-fermion systems

Neutron diffraction Pressure techniques

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. E. Dissanayake^*, F. Ye , W. Tian, and M. Matsuda ^†

Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

H. Muto, S. Suzuki, and T. Nakano

Graduate School of Science and Technology, Niigata University, Ikarashi, Niigata 950-2181, Japan

S. Watanabe

Department of Basic Sciences, Kyushu Institute of Technology, Kitakyushu, Fukuoka 804-8550, Japan

J. Gouchi and Y. Uwatoko

Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan

^*Present address: Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627, USA.
^†Corresponding author: matsudam@ornl.gov

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Vol. 105, Iss. 24 — 15 June 2022

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Figure 1
Temperature-pressure phase diagram of ${CePtSi}_{2}$ . The solid circles and triangles represent the data in Refs. [9, 12, 13] and the present results, respectively. The lines are guides to the eye.
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Figure 2
Contour maps of neutron diffraction intensity at a low- $Q$ region in the $(H 0 L)$ plane in ${CePtSi}_{2}$ measured at (a) 0.24 K and (b) 2.0 K, at ambient pressure. Magnetic peaks are observed at $(0.32, 0, 0.11)$ , $(- 0.32, 0, 0.11)$ , $(0.32, 0, - 0.11)$ , and $(- 0.32, 0, - 0.11)$ at 0.24 K. (c) and (d) Temperature dependence of the $(0.32, 0, 0.11)$ magnetic Bragg peak intensity. The solid line is the result of a fit to a power-law function.
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Figure 3
Two possible spin-density-wave structures for ${CePtSi}_{2}$ . The spin directions of $S_{1}$ and $S_{2}$ as well as those of $S_{3}$ and $S_{4}$ are parallel in model 1 (a) and antiparallel in model 2 (b), respectively. Model 1 was found to be the appropriate magnetic structure. Atomic coordinates of the atoms corresponding to $S_{1}$ , $S_{2}$ , $S_{3}$ , and $S_{4}$ are $S_{1}$ : $(0, 0.39465, 0.25)$ , $S_{2}$ : $(0, 0.60535, 0.75)$ , $S_{3}$ : $(0.5, 0.89465, 0.25)$ , and $S_{4}$ : $(0.5, 0.10535, 0.75)$ . (See the Supplemental Material [16].)
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Figure 4
Neutron diffraction intensities around $(0.32, 0, 0.11)$ , $(0.32, 2, 0.11)$ , and $(0.68, 1, 0.11)$ measured on HB-1A using a polycrystalline sample of ${CePtSi}_{2}$ . The background signal measured at 3 K was subtracted. A constant value was added to help the refinement using fullprof. The open circles are observed points. The bold solid line represents the result of the Rietveld refinement. The thin blue line is the difference between the observed and fitted intensities. The magnetic form factor for ${Ce}^{3 +}$ was used for the magnetic structure refinement. The residual intensity at $Q \sim 1.05 Å^{- 1}$ is too sharp for an actual magnetic peak and is most probably due to imperfect background subtraction.
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Figure 5
A $(0.32, 0, 0.11)$ magnetic Bragg peak measured at (a) 0.12 GPa, (b) 0.25 GPa, and (c) 0.4 GPa. The background intensities measured above $T_{SDW}$ are subtracted in (b) and (c). The solid lines are the results of fits to a Gaussian function. The data shown in (a)–(c) were measured at CORELLI diffractometer, HB-1, and HB-1A triple-axis spectrometers, respectively. (a) represents the $d$ -spacing dependence of integrated intensities obtained using the instrument view window in CORELLI, while (b) and (c) represent background subtracted $θ − 2 θ$ scans.
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Figure 6
Temperature dependence of the $(0.32, 0, 0.11)$ magnetic Bragg peak intensity measured at (a) 0.12 GPa and (b) 0.25 GPa. The solid lines are the fitting results to a power-law function. (c) Averaged magnetic moment around 0.3 K as a function of applied pressure. The dashed line is a guide to the eye.
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Physical Review B

covering condensed matter and materials physics

Pressure dependence of the magnetic ground state in ${CePtSi}_{2}$

S. E. Dissanayake, F. Ye, W. Tian, M. Matsuda, H. Muto, S. Suzuki, T. Nakano, S. Watanabe, J. Gouchi, and Y. Uwatoko

Phys. Rev. B 105, 245111 – Published 9 June 2022

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Physical Review B

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Pressure dependence of the magnetic ground state in CePtSi2

S. E. Dissanayake, F. Ye, W. Tian, M. Matsuda, H. Muto, S. Suzuki, T. Nakano, S. Watanabe, J. Gouchi, and Y. Uwatoko

Phys. Rev. B 105, 245111 – Published 9 June 2022

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Pressure dependence of the magnetic ground state in ${CePtSi}_{2}$