Strong spin frustration and negative magnetization in LnCu3(OH)6Cl3 (Ln = Nd and Sm) with triangular lattices: the effects of lanthanides.

Herbertsmithite- and kapellasite-type compounds with triangular lattices (i.e. Kagomé) as the most promising candidates for realizing the exotic quantum spin liquid (QSL) state have recently attracted significant attention in condensed matter physics and materials science but are often adversely affected by dimensional imperfections arising from significant cation mixing. Also, interaction mechanisms between the Kagomé lattices and ionic impurities remain unclear. Herein we report on the synthesis, crystal structures and magnetic properties of a new class of kapellasite-type compounds LnCu3(OH)6Cl3 (Ln = Nd and Sm) with two overlapped triangular lattices. These compounds are characterized by the triangular lattices of Cu2+ superimposed by another triangular lattice of paramagnetic Ln3+. The magnetic properties of LnCu3(OH)6Cl3 feature strong spin frustrations as well as antisymmetrical Dzyaloshinskii-Moriya interactions resulting in canted antiferromagnetic ordering with the Néel temperature (TN) of ∼20 K and ∼18 K for NdCu3(OH)6Cl3 and SmCu3(OH)6Cl3, respectively. Moreover, negative magnetization at low temperatures was firstly observed in Kagomé lattice compounds, arising from geometrical spin frustration and competing interactions within two overlapped triangular lattices.