Quantum magnetism in frustrated triangular lattices offers a platform for exploring exotic states, such as quantum spin liquids (QSLs) [1] and induced magnetism. This seminar investigates the contrasting magnetic behaviors of PrMgAl₁₁O₁₉ and NdMgAl₁₁O₁₉, hosting non-Kramers Pr³⁺ and Kramers Nd³⁺ ions, respectively, to elucidate how ion type shapes frustration and quantum dynamics.

In PrMgAl₁₁O₁₉, single-crystal X-ray diffraction reveals Pr³⁺ positional disorder, creating two distinct crystal electric field (CEF) environments [2]. This results in a double Schottky anomaly in specific heat, reflecting excitations within a split quasi-doublet [2]. Despite strong Ising anisotropy and antiferromagnetic interactions, no long-range order is observed down to 0.4 K. We interpret this as a quantum Ising magnet driven by an intrinsic transverse field [1, 3], distinct from a QSL [1]. Conversely, NdMgAl₁₁O₁₉ exhibits uniaxial anisotropy and weak antiferromagnetic coupling (Curie-Weiss temperature of -0.38 K) [4]. A specific heat anomaly at 81 mK suggests short-range correlations, while magnetization follows a Brillouin function, consistent with quasi-paramagnetic behavior from a Kramers doublet.

By comparing these systems, we highlight the pivotal role of non-Kramers versus Kramers ions in governing magnetic anisotropy and frustration. The talk will detail experimental approaches single-crystal growth, structural characterization, magnetization, and low temperature specific heat and discuss implications for exotic magnetic states.

References:

1. Balents, L., "Spin liquids in frustrated magnets," Nature 464, 199–208 (2010).
2. Kumar, S., et al., "Induced-quantum magnetism on a triangular lattice of non-Kramers ions in PrMgAl₁₁O₁₉," https://arxiv.org/abs/2410.07885 (2024)
3. Li, Y., et al., "Rare-Earth Triangular Lattice Spin Liquid: A Single-Crystal Study of TmMgGaO₄," Physical Review B 96, 214427 (2017).
4. Kumar, S., et al., "Magnetic Anisotropy and Frustration in the Triangular-Lattice Magnet NdMgAl₁₁O₁₉," unpublished manuscript (2025).