Ab initio prediction of a two-dimensional variant of the iridate IrO2

We propose an insulating two-dimensional phase of IrO2 , predicted by ab initio evolutionary algorithms. The predicted phase is a van der Waals crystal, in which Ir forms a triangular lattice, and is energetically competitive with the metastable spinel phase, observed experimentally. Electronic structure calculations show that the magnetic properties of this phase are highly nontrivial, with an almost perfect degeneracy of 120 degrees Neel and Y-stripe orders, and unusually soft magnetic moments. The resulting behavior, which we term easy plane anisotropy, is entirely different from what is realized in previously explored Kitaev honeycomb lattices. Our results thus suggest that IrO2 may be an ideal candidate to realize highly unusual magnetic properties.