Crystal field splitting, local anisotropy, and low-energy excitations in the quantum magnet ${\mathrm{YbCl}}_{3}$

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Crystal field splitting, local anisotropy, and low-energy excitations in the quantum magnet ${YbCl}_{3}$

G. Sala, M. B. Stone, Binod K. Rai, A. F. May, D. S. Parker, Gábor B. Halász, Y. Q. Cheng, G. Ehlers, V. O. Garlea, Q. Zhang, M. D. Lumsden, and A. D. Christianson

Phys. Rev. B 100, 180406(R) – Published 19 November 2019

Abstract

We study the correlated quantum magnet ${YbCl}_{3}$ with neutron scattering, magnetic susceptibility, and heat capacity measurements. The crystal field Hamiltonian is determined through simultaneous refinements of the inelastic neutron scattering and magnetization data. The ground-state doublet is well isolated from the other crystal field levels and results in an effective spin-1/2 system with local easy plane anisotropy at low temperature. Cold neutron spectroscopy shows low-energy excitations peaked at 0.5 meV that are consistent with nearest-neighbor antiferromagnetic correlations.

Received 23 July 2019
Revised 2 November 2019

DOI:https://doi.org/10.1103/PhysRevB.100.180406

Physics Subject Headings (PhySH)

Magnetism Magnons Specific heat Topological phases of matter

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

G. Sala ¹, M. B. Stone¹, Binod K. Rai ², A. F. May², D. S. Parker², Gábor B. Halász², Y. Q. Cheng¹, G. Ehlers ³, V. O. Garlea¹, Q. Zhang ¹, M. D. Lumsden¹, and A. D. Christianson^2,*

¹Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³Neutron Technologies Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

^*christiansad@ornl.gov

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Vol. 100, Iss. 18 — 1 November 2019

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Figure 1
Monoclinic crystal structure of ${YbCl}_{3}$ with $a = 6.7291 (3) Å$ ( $\hat{x}$ axis), $b = 11.6141 (9) Å$ ( $\hat{y}$ axis), $c = 6.3129 (3) Å$ , and $β = 110.5997 {(7)}^{\circ}$ obtained at 10 K. Refined structure parameters are further described in the SM [39]. (a) ${YbCl}_{3}$ structure consisting of alternating planes of ${Yb}^{3 +}$ cations (red spheres) forming a honeycomb lattice in the $a b$ plane, with ${Cl}^{-}$ anions (green spheres) separating the layers. (b) The crystal field environment surrounding the rare-earth ions consists of six Cl ions arranged in a distorted octahedron with $C_{2}$ point group symmetry. Note in this panel the octahedron has been rotated to coincide with that used for the crystal field modeling where the $\hat{y}$ axis is the axis of quantization (the $\hat{z}$ axis in the rotated coordinate system). (c) Single layer of Yb ions showing the honeycomb lattice in the monoclinic $a b$ plane with Yb-Yb distances at 10 K.
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Figure 2
Dynamic structure factor $S (| Q |, ℏ ω)$ of ${YbCl}_{3}$ collected with SEQUOIA with $E_{i} = 60$ meV at (a) $T = 5$ K and (b) $T = 95$ K. The nonmagnetic background determined from ${LuCl}_{3}$ has been subtracted. Crystal field excitations are visible at $ℏ ω = 21.04$ , 32.03, and 39.28 meV. (c) Comparison of the intensity of the CF transitions at $T = 5$ K and $T = 95$ K for ${YbCl}_{3}$ , in the momentum transfer range $Q = [2.5, 3.5] Å^{- 1}$ . The solid lines are the results of the CF analysis using Eq. (1). Horizontal black lines denote instrumental resolution. The $T = 5$ K data and model are offset by 0.3 units along the vertical axis. The data are scaled so that the strongest CF level has an intensity of 1.
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Figure 3
Top: Inverse magnetic susceptibility $χ$ as a function of temperature for polycrystalline ${YbCl}_{3}$ in the range $4 \leq T \leq 700$ K shown on a log-log scale for $H = 1 T$ . The red line is the result of a simultaneous fit of the CF model to the INS data (Fig. 2), the magnetic susceptibility, and the magnetization at 10 K. The top inset shows the calculated magnetization at 10 K compared with the experimental data. The bottom inset shows the calculated torque diagram using the CF parameters (green curve) at 2.1 K under an applied field of $5 T$ (red circle) in the $a b$ plane as measured in Ref. [37].
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Figure 4
Low-energy magnetic spectrum of ${YbCl}_{3}$ . All data have had the $T = 100$ K ${YbCl}_{3}$ measurement subtracted as a background. (a) Scattering intensity as a function of $Q$ (top axis) and $ℏ ω$ . (b) Scattering intensity as a function of $Q$ (top axis) integrated over $ℏ ω = [0.1, 1.2]$ meV. The solid line is the RMC calculation described in the text. (c) Scattering intensity as a function of $ℏ ω$ (bottom axis) integrated over $Q = [0.2, 2] Å^{- 1}$ .
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Physical Review B

covering condensed matter and materials physics

Crystal field splitting, local anisotropy, and low-energy excitations in the quantum magnet ${YbCl}_{3}$

G. Sala, M. B. Stone, Binod K. Rai, A. F. May, D. S. Parker, Gábor B. Halász, Y. Q. Cheng, G. Ehlers, V. O. Garlea, Q. Zhang, M. D. Lumsden, and A. D. Christianson

Phys. Rev. B 100, 180406(R) – Published 19 November 2019

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Physical Review B

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Crystal field splitting, local anisotropy, and low-energy excitations in the quantum magnet YbCl3

G. Sala, M. B. Stone, Binod K. Rai, A. F. May, D. S. Parker, Gábor B. Halász, Y. Q. Cheng, G. Ehlers, V. O. Garlea, Q. Zhang, M. D. Lumsden, and A. D. Christianson

Phys. Rev. B 100, 180406(R) – Published 19 November 2019

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Crystal field splitting, local anisotropy, and low-energy excitations in the quantum magnet ${YbCl}_{3}$