Interplay between local and itinerant magnetism in transition metal oxides: the role of anion magnetism*

Transition-metal oxides (TMOs) have been studied widely for their fascinating properties. Recently, neutron diffraction experiments and density-functional-theory (DFT) calculations found sizable magnetic moments on the oxygen anions in ferromagnetic SrRuO₃. In general, using appropriate functionals, DFT captures the magnetic properties of many TMOs. Here, we report comprehensive DFT calculations in a wide range of 3d-, 4d-, and 5d-TMOs and a few sulfides, aiming to elucidate the microscopic origin of anionic magnetization. We examine the local spin density of states, radial dependence of magnetization, and strain sensitivity. Cation-anion bond lengths play a major role in controlling the degree of anionic magnetization. However, we find a complex spin-density distribution in both coordinate and energy space, whereby the simple picture of TM d-orbitals overlapping the anions is not sufficient to account for the magnitude of anion magnetic moments. Anion magnetic moments range from zero (Heisenberg ferromagnets) to values that are comparable to cation magnetic moments (itinerant ferromagnets).