Magnetic Properties comparison of 3D Kitaev candidate materials beta and gamma Li2IrO3

Honeycomb iridates have been the focus of substantial interest due to the strong magnetic frustration that arises from their edge-shared bonding environment, which favors a strongly anisotropic Ising-like exchange between bonds. In materials with edge-shared IrO6 octahedra, spin-anisotropy of the exchange between neighboring effective spin-1/2 states is enhanced by the interference of the two exchange paths across the planar Ir-O-Ir bond. In the honeycomb lattice, such an interaction couples different orthogonal spin components for the three nearest neighbors; no single exchange direction can be simultaneously satisfied, leading to strong frustration which can be described by the Kitaev-model. We have recently synthesized two new structure that retains the same bonding environment as the honeycomb lattice, and extends this physics to three-dimensions. In this work, we compare the magnetic properties of these two novel structures, presenting evidences that their high temperature behavior can be explained by geometric g-factor constrains while the low temperature anisotropy and degeneracy of the ground state suggest the presence of spin anisotropic exchange.