Low-temperature magnetism and spin dynamics in the disordered triangular-lattice Yb${}^{3+}$ compound LiCaYb${}_5$(BO${}_3$)${}_6$

Abstract

The interplay between geometric frustration, spin--orbit coupling, and structural disorder can give rise to unconventional magnetic ground states in rare-earth triangular-lattice magnets. We report low-temperature magnetic and ${}^7$Li NMR investigations of the disordered triangular-lattice compound LiCaYb${}_5$(BO${}_3$)${}_6$ (LCYBO). Rietveld refinement confirms a hexagonal $P{6}_{5}22$ structure with partial Ca/Yb antisite disorder and fractional Li occupancy. Magnetic susceptibility and magnetization measurements indicate a well-isolated effective $J_{\mathrm{eff}}=1/2$ Kramers doublet with weak antiferromagnetic interactions (${\theta }_{\mathrm{CW}}\approx -0.54$~K). The specific heat reveals a weak anomaly near 0.43 K, suggesting the development of short-range correlated magnetism rather than conventional long-range order. ${}^7$Li NMR spectra broaden strongly upon cooling, consistent with increasingly inhomogeneous internal magnetic fields. The spin-lattice relaxation exhibits two relaxation components consistent with disorder-induced distributions of local magnetic environments arising from antisite disorder and competing exchange pathways. Our results establish LCYBO as a structurally disordered frustrated triangular-lattice magnet with correlated low-energy spin dynamics.

13 Pages, 10 figures