Realization of the anisotropic compass model on the diamond lattice of Cu2+ in CuAl2 O4

Abstract

Spin-orbit (SO) Mott insulators are regarded as a new paradigm of magnetic materials, whose properties are largely influenced by SO coupling and featured by highly anisotropic bond-dependent exchange interactions between the spin-orbital entangled Kramers doublets, as typically manifested in 5d iridates. Here, we propose that a very similar situation can be realized in cuprates when the Cu2+ ions reside in a tetrahedral environment, as in spinel compounds. Using first-principles electronic structure calculations, we construct a realistic model for the diamond lattice of the Cu2+ ions in CuAl2O4 and show that the magnetic properties of this compound are largely controlled by anisotropic compass-type exchange interactions that dramatically modify the magnetic ground state by lifting the spiral spin-liquid degeneracy and stabilizing a commensurate single-q spiral. © 2018 American Physical Society.