Magnetic properties of a spin-orbit entangled Jeff = 1/2 honeycomb lattice

The interplay between spin-orbit coupling, anisotropic magnetic interaction, frustration-induced quantum fluctuations and spin correlations can lead to novel quantum states with exotic excitations in rare-earth-based quantum magnets. Herein, we present the crystal structure, magnetization, electron spin resonance (ESR), specific heat, and nuclear magnetic resonance (NMR) experiments on the polycrystalline samples of Ba9Yb2Si6O24, in which Yb3+ ions form a perfect honeycomb lattice without detectable anti-site disorder. The magnetization data reveal antiferromagnetically coupled spin-orbit entangled Jeff = 1/2 degrees of freedom of Yb3+ ions in the Kramers doublet state. The ESR measurements reveal that the first excited Kramers doublet is 32.3(7) meV above the ground state. The specific heat results suggest the absence of any long-range magnetic order in the measured temperature range. Furthermore, the 29Si NMR results do not indicate any signature of magnetic ordering down to 1.6 K, and the spin-lattice relaxation rate reveals the presence of a field-induced gap that is attributed to the Zeeman splitting of Kramers doublet state in this quantum material. Our experiments detect neither spin freezing nor long-range magnetic ordering down to 1.6 K. The current results suggest the presence of short-range spin correlations in this spin-orbit entangled Jeff =1/2 rare-earth magnet on a honeycomb lattice.