Strong spin frustration and magnetism in kagomé antiferromagnets LnCu3(OH)6Br3(Ln = Nd, Sm, and Eu)

To study the effects of lanthanide ions on the geometrically frustrated antiferromagnets and their magnetic properties,we grew high-quality single crystals of LnCu3(OH)6Br3(Ln=Nd,Sm,and Eu) by hydrothermal method and studied their crystal structures and magnetic properties.The refinements of the crystal structure referred to the powder x-ray diffraction data show that LnCu3(OH)6Br3adopt a Kapellasite-type layer structure,which is isostructural to their chlorine analogue.Magnetic susceptibilities demonstrate that LnCu3(OH)6Br3have strong antiferromagnetic coupling and a pronounced magnetic frustration effect.Magnetization measurements indicate canted antiferromagnetic ordering of Cu2+ions around 16 K within the kagomé plane and weak ferromagnetic coupling.Moreover,shoulder-like anomalies in specific heat around 16 K could be a signature of emergent of magnetic ordering.The low-temperature negative magnetization and specific heat of LnCu3(OH)6Br3(Ln=Nd,Sm,and Eu) indicate that Ln3+ions induce more exotic magnetic ground state properties.