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arXiv · 2507.12592

Quenched Disorder in the Triangular Lattice Antiferromagnet YbZn$_2$GaO$_5$

Leshan Zhao·Tong Chen·Matthew B. Stone·Qiang Zhang·Colin L. Sarkis·S. M. Koohpayeh·Collin Broholm
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Abstract

We investigate the crystal electric field (CEF) excitations of Yb$^{3+}$ ions in powder samples of the triangular-lattice rare-earth-based antiferromagnet YbZn$_2$GaO$_5$ using inelastic neutron scattering (INS). Three CEF excitations from the ground-state Kramers doublet were observed, each exhibiting significant broadening beyond instrumental resolution. Combining temperature-dependent INS and neutron powder diffraction, we identify a significant static contribution to this broadening and attribute it to heterogeneous coordination of Yb$^{3+}$ ions due to Ga$^{3+}$/Zn$^{2+}$ site mixing. Rietveld refinement of neutron powder diffraction indicates that 35% of Ga occupies the Zn site and 60% of Zn occupies the Ga site. We show with a point charge model for the CEF Hamiltonian that heterogeneous coordination of Yb$^{3+}$ ions leads to broadened CEF peaks. First-principles calculations demonstrate that the random Ga$^{3+}$/Zn$^{2+}$ distribution can produce the distortions of the YbO$_6$ octahedra observed from neutron diffraction. Because the documented heterogeneity will extend to exchange interactions, our results suggest that disorder is a significant factor in the unusual magnetism previously reported in YbZn$_2$GaO$_5$, including broad low-energy magnetic excitations and the absence of magnetic ordering down to 0.3K.

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Leshan Zhao, Tong Chen, Matthew B. Stone, Qiang Zhang, Colin L. Sarkis, S. M. Koohpayeh, Collin Broholm. 2025-07-16. Quenched Disorder in the Triangular Lattice Antiferromagnet YbZn$_2$GaO$_5$. https://arxiv.org/abs/2507.12592

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