CommunicationSurface ferromagnetism in HfO2 induced by excess oxygen

- A d0 ferromagnetism mechanism of solid state matters is addressed.
- The surfaces electronic states are with large 2p spin exchange energy.
- A possible origin of ferromagnetism observed in HfO2 is discussed.

First-principles numerical simulations based on density functional theory are performed to examine surface electronic and magnetic properties of cubic, tetragonal, and monoclinic HfO2 with low index terminations. Our systematic calculations reveal that i) stoichiometric surfaces and Hf rich non-stoichiometric surfaces are non magnetic, and ii) O rich non-stoichiometric surfaces are ferromagnetic and metallic. The ferromagnetism found here is attributed to O surface electronic states with large O 2p spin exchange energy. This finding provides a novel pathway to d0 ferromagnetism for simple oxides with no magnetic ions involved. We also calculate the surface energy and discuss a recent controversial issue of ferromagnetism observed experimentally in HfO2.