Frustration enhanced by Kitaev exchange in a $\boldsymbol{\tilde{j}_{\text{eff}}=\frac12}$ triangular antiferromagnet

TL;DR

This paper demonstrates that in Na$_2$BaCo(PO$_4$)$_2$, Kitaev exchange enhances frustration in a $ ilde{j}_{ ext{eff}}=1/2$ triangular antiferromagnet, leading to strong magnetic correlations above ordering temperatures, indicating potential for a Kitaev spin-liquid state.

Contribution

It reveals the role of ferromagnetic Kitaev exchange in increasing frustration and stabilizing a $ ilde{j}_{ ext{eff}}=1/2$ state in a triangular antiferromagnet, suggesting a new candidate for Kitaev spin liquids.

Findings

Emergence of $ ilde{j}_{ ext{eff}}=1/2$ moments in Na$_2$BaCo(PO$_4$)$_2$

Magnetic correlations develop well above ordering temperatures

Kitaev exchange acts as an additional source of frustration

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 ${\tilde{j}_{\text{eff}}=\frac12}$ moments in the triangular-lattice magnet Na$_2$BaCo(PO$_4$)$_2$. 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 the $\tilde{j}_{\text{eff}}=\frac12$ ground state, theory identifies ferromagnetic Kitaev exchange anisotropy as additional frustrating agent, altogether putting forward Na$_2$BaCo(PO$_4$)$_2$ as a promising Kitaev spin-liquid material.