Ba3BiPbREO(BO3)4 (RE =Pr, Nd, Gd, Dy): Two-Dimensional Rare-Earth Antiferromagnets with Geometrically-Perfect Triangular Lattice Directed by Triangular BO3 Unit

The synthesis of novel two-dimensional (2D) triangular frustrated compounds are important for providing various platforms to investigate exotic quantum magnetism. Here, we successfully synthesised a series of RE-based magnetic compounds Ba3BiPbREO(BO3)4 (RE = Pr, Nd, Gd, Dy) with a geometrically-perfect 2D triangular lattice directed by triangular BO3 unit. These compounds stabilise 2D layered structures in the hexagonal (P63/mmc) crystal system, where magnetic ions are linked by BO3 to form a perfect triangular frustrated lattice. The magnetisation susceptibility results show that all synthesised compounds Ba3BiPbREO(BO3)4 exhibit dominant antiferromagnetic (AFM) interactions, with no long-range order (LRO) down to 2 K, which is further confirmed by specific heat measurements. Additionally, their thermal stability, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and Ultraviolet−visible-near-infrared (UV−Vis−NIR) diffuse reflectance spectra are also reported. This work provides a series of RE-based magnetic compounds with a two-dimensional triangular frustrated lattice, offering novel model materials for further investigation on rare-earth-based frustrated magnetism.