Disordered ground state in the spin-orbit coupled ${J}_{\mathrm{eff}}$ = $\frac{1}{2}$ distorted honeycomb magnet ${\mathrm{BiYbGeO}}_{5}$

Disordered ground state in the spin-orbit coupled $J_{eff}$ = $\frac{1}{2}$ distorted honeycomb magnet ${BiYbGeO}_{5}$

S. Mohanty, S. S. Islam, N. Winterhalter-Stocker, A. Jesche, G. Simutis, Ch. Wang, Z. Guguchia, J. Sichelschmidt, M. Baenitz, A. A. Tsirlin, P. Gegenwart, and R. Nath

Phys. Rev. B 108, 134408 – Published 9 October 2023

Abstract

We delineate quantum magnetism in the strongly spin-orbit coupled distorted honeycomb lattice antiferromagnet ${BiYbGeO}_{5}$ . Our magnetization and heat capacity measurements reveal that its low-temperature behavior is well described by an effective $J_{eff} = \frac{1}{2}$ Kramers doublet of ${Yb}^{3 +}$ . The ground state is nonmagnetic with a tiny spin gap. Temperature-dependent magnetic susceptibility, magnetization isotherm, and heat capacity can be modeled well assuming isolated spin dimers with anisotropic exchange interactions $J_{Z} ≃ 2.6$ K and $J_{XY} ≃ 1.3$ K. Heat capacity measurements backed by muon spin relaxation suggest the absence of magnetic long-range order down to at least 80 mK both in zero field and in applied fields. This sets ${BiYbGeO}_{5}$ apart from ${Yb}_{2} {Si}_{2} O_{7}$ , with its unusual regime of magnon Bose-Einstein condensation, and suggests negligible interdimer couplings, despite only a weak structural deformation of the honeycomb lattice.

Received 17 May 2023
Revised 21 September 2023
Accepted 22 September 2023

DOI:https://doi.org/10.1103/PhysRevB.108.134408

Physics Subject Headings (PhySH)

Antiferromagnetism Magnetic interactions Magnetic phase transitions Spin-orbit coupling

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Mohanty ¹, S. S. Islam ¹, N. Winterhalter-Stocker², A. Jesche ², G. Simutis³, Ch. Wang⁴, Z. Guguchia⁴, J. Sichelschmidt ⁵, M. Baenitz ⁵, A. A. Tsirlin ⁶, P. Gegenwart ², and R. Nath ^1,*

¹School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram 695551, India
²Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
³Laboratory for Neutron and Muon Instrumentation, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
⁴Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
⁵Max Planck Institute for Chemical Physics of Solids, Nothnitzer Strasse 40, 01187 Dresden, Germany
⁶Felix Bloch Institute for Solid-State Physics, Leipzig University, 04103 Leipzig, Germany

^*rnath@iisertvm.ac.in

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Vol. 108, Iss. 13 — 1 October 2023

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Figure 1
(a) Crystal structure of ${BiYbGeO}_{5}$ viewed along the $a$ axis, showing well-separated honeycomb layers formed by edge-shared ${YbO}_{7}$ polyhedra. (b) A section of the honeycomb layer projected onto the $a c$ plane highlights the short ${Yb}^{3 +} - {Yb}^{3 +}$ distance that leads to spin dimerization.
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Figure 2
Powder XRD pattern (open circles) at $T = 300$ K for (a) ${BiYbGeO}_{5}$ and (b) ${BiYGeO}_{5}$ . The black solid line represents the Rietveld fit of the data. Expected Bragg peak positions are indicated by green vertical bars, and the solid blue line at the bottom denotes the difference between experimental and calculated intensities. The goodness of fit is $χ^{2} ≃ 7.5$ and 7.2, respectively.
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Figure 3
(a) $χ (T)$ of ${BiYbGeO}_{5}$ measured in different fields. The solid line represents the simulation for isolated spin dimers with anisotropic interactions ( $J_{z} = 2.6$ K and $J_{xy} = 1.3$ K) for $μ_{0} H = 0.01$ T. Inset: CW fit to the low- $T 1 / χ$ data (after subtracting the Van Vleck contribution). (b) $M$ vs $H$ and $d M / d H$ vs $H$ in the left and right $y$ axes, respectively, measured at $T = 0.4$ K. The horizontal dashed line marks the Van Vleck contribution. The solid line shows the simulation.
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Figure 4
(a) $C_{p}$ vs $T$ for ${BiYbGeO}_{5}$ measured in different applied fields. The solid line represents $C_{ph} (T)$ of the nonmagnetic analog ${BiYGeO}_{5}$ . Inset: Zero-field $C_{p}$ vs $T$ in the low-temperature regime. The solid line represents the nuclear contribution $C_{n}$ . (b) Magnetic heat capacity $C_{mag}$ vs $T$ in different magnetic fields. Inset: Magnetic entropy $S_{mag}$ vs $T$ in different magnetic fields. (c) Electronic Schottky contribution [ $C_{p} (H) - C_{p} (0)$ ] vs $T$ along with the fit using Eq. (1). Inset: $Δ / k_{B}$ and $f$ vs $H$ in the left and right $y$ axes, respectively. The solid line represents the straight line fit to $Δ / k_{B}$ vs $H$ .
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Figure 5
Muon decay asymmetry vs time in zero field at four different temperatures, with solid lines being the exponential fits. Inset: $λ$ vs $T$ from both the GPS and HAL spectrometers together with the fit using an activated behavior (solid line) with $Δ_{μ} / k_{B} ≃ 1.7$ K.
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Figure 6
Magnetic heat capacity $C_{mag}$ vs $T$ , measured down to 0.08 K in different fields. The solid and dashed lines represent simulated curves for an isolated spin- $\frac{1}{2}$ dimer with either isotropic or anisotropic exchange interactions. We also show the simulation for the anisotropic spin- $\frac{1}{2}$ dimer in an applied field of 1.25 T where powder averaging was taken into account. Inset: Zero-field $C_{mag}$ vs $T$ ; the solid line is an exponential fit with $Δ / k_{B} = 1.5 (1)$ K.
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Physical Review B

covering condensed matter and materials physics

Disordered ground state in the spin-orbit coupled $J_{eff}$ = $\frac{1}{2}$ distorted honeycomb magnet ${BiYbGeO}_{5}$

S. Mohanty, S. S. Islam, N. Winterhalter-Stocker, A. Jesche, G. Simutis, Ch. Wang, Z. Guguchia, J. Sichelschmidt, M. Baenitz, A. A. Tsirlin, P. Gegenwart, and R. Nath

Phys. Rev. B 108, 134408 – Published 9 October 2023

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Physical Review B

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Disordered ground state in the spin-orbit coupled Jeff = 12 distorted honeycomb magnet BiYbGeO5

S. Mohanty, S. S. Islam, N. Winterhalter-Stocker, A. Jesche, G. Simutis, Ch. Wang, Z. Guguchia, J. Sichelschmidt, M. Baenitz, A. A. Tsirlin, P. Gegenwart, and R. Nath

Phys. Rev. B 108, 134408 – Published 9 October 2023

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Disordered ground state in the spin-orbit coupled $J_{eff}$ = $\frac{1}{2}$ distorted honeycomb magnet ${BiYbGeO}_{5}$