Octa-Kagomé Lattice Compounds Showing Quantum Critical Behaviors: Spin Gap Ground State versus Antiferromagnetic Ordering

Search for a new
geometrically frustrated lattice is a great challenge.
Herein, we report on a successful synthesis of two new layered compounds
BiOCu2(XO3)­(SO4)­(OH)·H2O [X = Te (1) and Se (2)] with a new type
of geometrically frustrated lattice (i.e., the octa-kagomé
lattice) between kagomé and star motifs. Magnetic measurements
confirmed that 1 exhibits a spin gap ground state, while 2 possesses a typical antiferromagnetic ordering at low-temperature.
Such different magnetic behaviors between two isostructural compounds
are suggested to originate from a slightly structural modification
induced by nonmagnetic XO3 anionic groups. Theoretical
simulations suggest that the origin of gapped ground state in 1 may be due to the dimerization of Cu2+ ions,
while 2 may break the limiting of such dimerization,
leading to an antiferromagnetic ordering.