Frustration enhanced by Kitaev exchange in a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mover accent="true"><mml:mi>j</mml:mi><mml:mo></mml:mo></mml:mover><mml:mtext>eff</mml:mtext></mml:msub><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:mrow></mml:math> triangular antiferromagnet
C. Wellm, Willi Roscher, J. Zeisner, A. Alfonsov, Ruidan Zhong, R. J. Cava, A. Savoyant, R. Hayn, Jeroen van den Brink, B. Büchner, Oleg Janson, V. Kataev
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 ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{j}}_{\text{eff}}=\frac{1}{2}$ moments in the triangular-lattice magnet ${\mathrm{Na}}_{2}\mathrm{Ba}\mathrm{Co}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$. 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 ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{j}}_{\text{eff}}=\frac{1}{2}$ ground state, theory identifies ferromagnetic Kitaev exchange anisotropy as an additional frustrating agent, altogether putting forward ${\mathrm{Na}}_{2}\mathrm{Ba}\mathrm{Co}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ as a promising Kitaev spin-liquid material.