Synthesis, structure, and magnetic properties of extended 2-D triangular lattices

Abstract

A series of pure iron jarosites (formula AFe₃(OH)₆(TO₄)₂) possessing the paradigmatic kagomé lattice has been prepared stoichiometrically pure through the use of a redox-based hydlrothermal synthetic strategy. This synthetic method allows us grow single crystals from which we fully characterize the structure and magnetic properties. Iron jarosites show signature spin frustrated behavior, indicated by a large Curie-Weiss constant, [theta] [approx.] -800 K, with a transition temperature, ... narrowly ranging from 56 - 65 K. Long-range antiferromagnetic order is due to a canted spin structure developed from the Dzyaloshinsky-Moriya (DM) interaction. Although the DM interaction energy is only 1.2 cm⁻¹, this is large enough to give rise to a 3-D magnetic structure, precluding the ability to study the ground state physics of a purely 2-D frustrated spin system. Copper hydroxy-bridged triangular species have been prepared and characterized both structurally and magnetically. Overall, the nearest-neighbor exchange interaction is found to be antiferromagnetic in each compound, with [Theta] ranging from -18 to -300 K, although the 1-D material lindgrenite, Cu₃(OH)₂)(MoO₄)₂, and the kagomé-lattice-containing material clinoatacamite, Cu₂(OH)₃Cl, show 3-D long-range ferromagnetic order. The compound zinc paratacamite presents the hallmark of an S = 1/2 Cu²⁺ compound possessing the kagomé lattice. This compound has magnetically isolated layers, and we find no evidence for magnetic ordering to temperatures down to 2 K, despite strong nearest-neighbor antiferromagnetic coupling, indicated by [Theta] [approx.] -300 K.