Frustration enhanced by Kitaev exchange in a ̃ 𝑗 eff= 1/2 triangular antiferromagnet

Abstract

Triangular Heisenberg antiferromagnets are prototypes of geometric frustration, even if for nearest-neighbor interactions quantum fluctuations are not usually strong enough to destroy magnetic ordering: stronger frustration is required to stabilize a spin-liquid phase. On the basis of static magnetization and electron spin resonance measurements, we demonstrate the emergence of 𝑗 eff=1/2 moments in the triangular-lattice magnet Na2⁢Ba⁢Co⁢(P⁢O4)2. These moments are subject to an extra source of frustration that causes magnetic correlations to set in far above both the magnetic ordering and Weiss temperatures. Corroborating thẽ𝑗 eff=1/2 ground state, theory identifies ferromagnetic Kitaev exchange anisotropy as an additional frustrating agent, altogether putting forward Na2⁢Ba⁢Co⁢(P⁢O4)2 as a promising Kitaev spin-liquid material.