The effect of octahedral distortions on the electronic properties and magnetic interactions in O3 NaTMO(2) compounds (TM = Ti–Ni & Zr–Pd)

The interplay between the coordination environment and magnetic properties in O3 layered sodium transition metal oxides (NaTMO(2)) is a fascinating and complex problem. Through detailed and comprehensive density functional investigations on O3 NaTMO(2) compounds, we demonstrate that the TM ions in O3 NaMnO(2), NaFeO(2) and NaCoO(2) adopt a high spin state. Structurally, NaMnO(2) and NaPdO(2) undergo Jahn–Teller distortions while NaNbO(2) undergoes puckering distortion. Furthermore, in addition to Jahn–Teller distortion, NaPdO(2) exhibits charge disproportionation as it contains Pd(2+), Pd(3+) and Pd(4+) species. These distortions stabilize the inter-plane ferromagnetism. Additionally, the inter-plane ferromagnetic coupling is stabilized by kinetic p–d exchange mechanism in undistorted NaCoO(2), NaNiO(2) and NaTcO(2). The intra-plane coupling in this family of compounds on the other hand was found to be generally weak. Only NaMnO(2), NaNiO(2) and NaTcO(2) are predicted to show bulk ferromagnetism with estimated Curie temperatures below ∼50 K.