Ba9RE2(SiO4)(6) (RE = Ho-Yb): A Family of Rare-Earth-Based Honeycomb-Lattice Magnets

Rare-earth (RE)-based honeycomb-lattice materials withstrong spin-orbitcoupled J (eff) = 1/2 moments have attractedgreat interest as a platform to realize the Kitaev quantum spin liquid(QSL) state. Herein, we report the discovery of a family of RE-basedhoneycomb-lattice magnets Ba9RE2(SiO4)(6) (RE = Ho-Yb), which crystallize into the rhombohedralstructure with the space group R3 . In theseserial compounds, magnetic RE3+ ions are arranged on aperfect honeycomb lattice within the ab-plane andstacked in the "ABCABC"-type fashion along the c-axis. All synthesized Ba9RE2(SiO4)(6) (RE = Ho-Yb) polycrystals exhibit thedominant antiferromagnetic interaction and absence of magnetic orderdown to 2 K. In combination with the magnetization and electron spinresonance results, magnetic behaviors are discussed for the compoundswith different RE ions. Moreover, the as-grown Ba9Yb2(SiO4)(6) single crystals show large magneticfrustration with frustration index f = & theta;(CW)/T (N) > 8 and no long-rangemagneticordering down to 0.15 K, being a possible QSL candidate material.These series of compounds are attractive for exploring the exoticmagnetic phases of Kitaev materials with 4f electrons. The honeycomb-lattice magnet Ba9Yb2(SiO4)(6) crystallizes into therhombohedralstructure with the space group R3 , where themagnetic Yb3+ ions locate on a perfect honeycomb latticewith an equal nearest Yb3+-Yb3+ intralayerdistance in the ab-plane. The low-temperature specificheat results show that no long-range magnetic ordering is detecteddown to 0.15 K.