Frustrated Magnetism in a 2-D Ytterbium Fluoride

Geometric frustration of magnetic ions combines with spin-orbit coupling and structural disorder to give rise to potentially, highly entangled magnetic states such as quantum spin liquids. While fluoride-based frustrated magnets are common in the d-block, in the f-block, fluoride-based frustrated magnets are extremely rare. Herein, we report the synthesis of KYb₂F₅SO₄, a fluoride-based distorted triangular lattice antiferromagnet with no structural disorder but significant geometric distortion from an ideal triangular lattice. In KYb₂F₅SO₄, no long-range ordering can be observed down to 0.10 K, and the low-temperature Curie-Weiss temperature θ_cw = -0.46(2) K yields a frustration parameter of greater than 4.6. The magnetic entropy released at low temperature indicates an effective spin-1/2 Kramer's doublet ground state. However, the low saturation field and incomplete recovery of magnetic entropy down to 0.10 K under zero-field imply weak quantum entanglement.