Spin-Glass Ground State in a Triangular-Lattice Compound ${\mathrm{YbZnGaO}}_{4}$

Spin-Glass Ground State in a Triangular-Lattice Compound ${YbZnGaO}_{4}$

Zhen Ma, Jinghui Wang, Zhao-Yang Dong, Jun Zhang, Shichao Li, Shu-Han Zheng, Yunjie Yu, Wei Wang, Liqiang Che, Kejing Ran, Song Bao, Zhengwei Cai, P. Čermák, A. Schneidewind, S. Yano, J. S. Gardner, Xin Lu, Shun-Li Yu, Jun-Ming Liu, Shiyan Li, Jian-Xin Li, and Jinsheng Wen

Phys. Rev. Lett. 120, 087201 – Published 22 February 2018

Abstract

We report on comprehensive results identifying the ground state of a triangular-lattice structured ${YbZnGaO}_{4}$ as a spin glass, including no long-range magnetic order, prominent broad excitation continua, and the absence of magnetic thermal conductivity. More crucially, from the ultralow-temperature ac susceptibility measurements, we unambiguously observe frequency-dependent peaks around 0.1 K, indicating the spin-glass ground state. We suggest this conclusion holds also for its sister compound ${YbMgGaO}_{4}$ , which is confirmed by the observation of spin freezing at low temperatures. We consider disorder and frustration to be the main driving force for the spin-glass phase.

Received 30 November 2017
Revised 12 January 2018

DOI:https://doi.org/10.1103/PhysRevLett.120.087201

Physics Subject Headings (PhySH)

Quantum spin liquid Spin waves Thermal conductivity

Spin glasses

AC susceptibility measurements DC susceptibility measurements Neutron scattering Specific heat measurements

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Zhen Ma¹, Jinghui Wang¹, Zhao-Yang Dong¹, Jun Zhang², Shichao Li¹, Shu-Han Zheng¹, Yunjie Yu², Wei Wang¹, Liqiang Che³, Kejing Ran¹, Song Bao¹, Zhengwei Cai¹, P. Čermák⁴, A. Schneidewind⁴, S. Yano⁵, J. S. Gardner^5,6, Xin Lu^3,7, Shun-Li Yu^1,7,*, Jun-Ming Liu^1,7, Shiyan Li^2,7,†, Jian-Xin Li^1,7,‡, and Jinsheng Wen^1,7,§

¹National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
²State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
³Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
⁴Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstr. 1, 85748 Garching, Germany
⁵National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan
⁶Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
⁷Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China

^*slyu@nju.edu.cn
^†shiyan_li@fudan.edu.cn
^‡jxli@nju.edu.cn
^§jwen@nju.edu.cn

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Vol. 120, Iss. 8 — 23 February 2018

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Figure 1
(a) Schematic crystal structure for ${YbZnGaO}_{4}$ and ${YbMgGaO}_{4}$ . (b) Top view of the triangular layer of ${YbO}_{6}$ octahedra. (c) dc magnetic susceptibility for fields applied parallel ( $χ_{| |}$ ) and perpendicular ( $χ_{⊥}$ ) to the $c$ axis for the single crystal, and polycrystalline sample ( $χ_{p}$ ), measured with a 0.1-T field. The data have been corrected by the Van Vleck paramagnetic susceptibility, as discussed in Ref. [24]. The solid line is the averaged susceptibility $χ_{ave}$ . The inset shows the inverse susceptibility and the accompanying Curie-Weiss fits. (d) Magnetic specific heat $C_{m}$ measured at zero and 9-T fields. $C_{m}$ is obtained by subtracting the contribution from the lattice using a nonmagnetic reference sample ${LuZnGaO}_{4}$ . Solid lines are fits to the data described in the main text. The inset shows the zero-field magnetic entropy $S_{m}$ , obtained using $S_{m} = \int_{0}^{T} C_{m} / T d T$ . The dashed line indicates $R \ln 2$ ( $R = the ideal$ gas constant).
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Figure 2
(a) and (b) are contour maps of the INS spectra at $E = 0.3$ and 0.6 meV, respectively, measured at $T = 0.47 K$ . The maps are obtained by plotting together a series of constant-energy scans along the [ $H$ , 0, 0] direction with a step size of 0.1 r.l.u., and an interval of 0.1 r.l.u. along the [0, $K$ , 0] direction. Solid lines indicate Brillouin zone boundaries. The additional bright feature around ( $- 0.5$ , 0.5, 0) in (a) does not represent a magnetic Bragg peak [24]. (c) Magnetic dispersion along the $M_{1} - K - Γ_{1}$ and $Γ_{1} - M_{2} - Γ_{2}$ directions as illustrated by the arrows in (a). The dispersion is obtained by plotting together a series of constant-energy scans as shown in (d) and (e), with an energy interval of 0.1 meV. The dashed line indicates constant-energy scans at $E = 0.8 meV$ . In (d) and (e), lines through the data are the calculated results extracted from Fig. 3. Errors represent 1 standard deviation throughout the Letter.
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Figure 3
(a) Contour map of the calculated spectra at $E = 0.6 meV$ . (b) Calculated dispersions along the two high-symmetry paths illustrated in (a).
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Figure 4
(a) Thermal conductivity results on ${YbZnGaO}_{4}$ under zero and 9-T magnetic fields applied parallel to the $c$ axis. The dashed line is a fit to the data described in the main text. For comparison, results on ${YbMgGaO}_{4}$ and the nonmagnetic reference compound ${LuMgGaO}_{4}$ are also plotted [12]. (b) Frequency dependence of the freezing temperature for both ${YbZnGaO}_{4}$ and ${YbMgGaO}_{4}$ , extracted from the temperature dependence of the real part of the ac susceptibility $χ^{'}$ shown in (c) and (d). Lines through data are guides to the eye. In the insets of (c) and (d), $χ^{'}$ in an extended temperature range up to 4 K is plotted. Dashed lines indicate the Curie-Weiss fits for the 100-Hz data.
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Physical Review Letters

Spin-Glass Ground State in a Triangular-Lattice Compound YbZnGaO4

Zhen Ma, Jinghui Wang, Zhao-Yang Dong, Jun Zhang, Shichao Li, Shu-Han Zheng, Yunjie Yu, Wei Wang, Liqiang Che, Kejing Ran, Song Bao, Zhengwei Cai, P. Čermák, A. Schneidewind, S. Yano, J. S. Gardner, Xin Lu, Shun-Li Yu, Jun-Ming Liu, Shiyan Li, Jian-Xin Li, and Jinsheng Wen

Phys. Rev. Lett. 120, 087201 – Published 22 February 2018

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Spin-Glass Ground State in a Triangular-Lattice Compound ${YbZnGaO}_{4}$