Post-perovskite CaIrO3: A j = 1/2 quasi-one-dimensional antiferromagnet

The 5d5 iridate CaIrO3 is isostructural with the post-perovskite phase ofMgSiO3, recently shown to occur under extreme pressure in the lower Earth’smantle. It therefore serves as an analog of post-perovskiteMgSiO3 for awide variety of measurements at ambient conditions or achievable with conventional multianvile pressure modules. By multireference configuration-interaction calculations we here provide essential information on the chemical bonding and magnetic interactions in CaIrO3. We predict a large antiferromagnetic superexchange of 120 meV along the c axis, the same size with the interactions in the cuprate superconductors, and ferromagnetic couplings smaller by an order of magnitude along a. CaIrO3 can thus be regarded as a j=1/2 quasi-one-dimensional antiferromagnet. While this qualitatively agrees with the stripy magnetic structure proposed by resonant x-ray diffraction, the detailed microscopic picture emerging from our study, in particular, the highly uneven admixture of t2g components, provides a clear prediction for resonant inelastic x-ray scattering experiments.