Absence of magnetic order and emergence of unconventional fluctuations in the Jeff=12 triangular-lattice antiferromagnet YbBO3

Abstract

We present the ground state properties of a new quantum antiferromagnet, YbBO 3 , in which the isotropic Yb 3+ triangular layers are separated by a nonmagnetic layer of partially occupied B and O(2) sites. The magnetization and heat capacity data establish a spin-orbit entangled effective spin J eff = 1 2 state of Yb 3+ ions at low temperatures, interacting antiferromagnetically with an intralayer coupling J/k B 0.53 K. The absence of oscillations and a 1/3 tail in the zero-field muon asymmetries rules out the onset of magnetic long-range order as well as spin freezing down to 20 mK. An anomalous broad maximum in the temperature-dependent heat capacity with an unusually reduced value and a broad anomaly in the zero-field muon depolarization rate centered at T * 0.7J/k B provide compelling evidence for a wide fluctuating regime (0.2 T /J 1.5) with slow relaxation. We infer that the fluctuating regime is a universal feature of highly frustrated triangular-lattice antiferromagnets while the absence of magnetic long-range order is due to perfect two-dimensionality of the spin lattice protected by nonmagnetic site disorder.

Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy–Yb): A Family of Rare-Earth-Based Layered Triangular Lattice Magnets

“…From that, Ba 6 Yb 2 Ti 4 O 17 as an example, the intralayers' exchange interaction and dipolar interaction are D ∼ 0.020 K and J nn ∼ −0.47 K, and here the distance ratio for the Yb 3+ ion between the interlayer and intralayer ones is δ = d 1 /d 0 ∼ 1.25, which is larger than ∼1.17 for the YbBO 3 compound. 35 Moreover, the estimated J/k B (∼0.47 K) in Ba 6 Yb 2 Ti 4 O 17 is comparable to that of YbBO 3 (∼0.53 K). As another typical feature, the 'AA' type stacking fashion of the layered triangular-lattice in Ba 6 Yb 2 Ti 4 O 17 does not introduce the additional geometric frustration from the stacking order; this is different from the 'ABC' stacking fashion in NaBaYb(BO 3 ) 2 and NaYbS 2 compounds.…”