Speaker
Description
Triangular-lattice antiferromagnets (TLAFs) provide a versatile platform for exploring frustrated magnetism, where geometric constraints inhibit conventional long-range order and foster exotic quantum states [1]. In these systems, the interplay between spin–orbit coupling and crystal electric field effects induces markedly different behaviors between Kramers and non-Kramers ions; Kramers ions (e.g., Nd$^{3+}$, Yb$^{3+}$) generally exhibit robust single-ion anisotropy and pronounced quantum fluctuations [1]. Within this context, the ReMgAl$_{11}$O$_{19}$ family has garnered considerable interest as an ideal platform for investigating frustrated magnetism [2-3]. Our work centers on NdMgAl$_{11}$O$_{19}$, a representative of this series. High-quality single crystals were synthesized using the optical floating zone method, and comprehensive measurements including magnetic susceptibility, magnetization, and specific heat were performed down to $45$ mK.
Our findings reveal that Nd$^{3+}$ ions in NdMgAl$_{11}$O$_{19}$ realize a Kramers doublet ground state characterized by strong uniaxial anisotropy along the crystallographic $c$-axis. Curie–Weiss analysis yields small negative temperatures, indicative of weak antiferromagnetic coupling. Moreover, a sharp specific heat anomaly near $81$ mK suggests either partial spin freezing or the emergence of short-range correlations. Under moderate magnetic fields, the low-temperature thermodynamics are well described by a two-level Schottky model arising from the Zeeman splitting of the Nd$^{3+}$ doublet, with the extracted $g$-factor in good agreement with magnetization fits.
These results position NdMgAl$_{11}$O$_{19}$ at the group of TLAF frustrated magnetism and rare-earth single-ion anisotropy, offering insights into the interplay of quantum fluctuations and emergent phenomena in complex magnetic systems.
References
[1] L. Savary and L. Balents, “Quantum spin liquids: a review,” Reports on Progress in Physics, vol. 80, no. 1. IOP Publishing, p. 016502, Nov. 08, 2016. https://doi.org/10.1088/0034-4885/80/1/016502
[2] B. Gao et al., “Spin Excitation Continuum in the Exactly Solvable Triangular-Lattice Spin Liquid CeMgAl11O19,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2408.15957
[3] S. Kumar et al., “Induced quantum magnetism on a triangular lattice of non-Kramers ions in PrMgAl11O19,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2410.07885
