Periodic oxygen-defective ZrO2-x films with room-temperature ferromagnetism produced by precisely controlling oxidation of metallic Zr foil

Ferromagnetism can be induced by introducing oxygen vacancies into metallic oxides. The oxygen deficiencies introduced into ZrO2 samples thus far have been present in unquantifiable concentrations and randomly scat-tered near the surface. We successfully produced room-temperature-ferromagnetic 9 mu m-thick ZrO2-x films via a stepwise oxidation process consisting of annealing metallic Zr foil in air and under a controlled oxygen partial pressure. The ZrO2-x films are composed of a periodic structure with a spacing of 3-4 nm; this structure orig-inated from the presence and absence of oxygen deficiencies. The unique structure in the ZrO2-x phase consisting of the periodic arrangements of oxygen deficiencies can be produced by the stepwise oxidation using Zr metal. Our proposed process should open the door for new applications of defect-driven ferromagnetic films of undoped magnetic oxides with a periodic oxygen-defective structure.