Hybridized microstructures of oxygen‐defective HfO2−x films produced by controlling oxidation of metallic Hf foil.

We successfully produced a dopant‐free oxygen‐defective HfO2−<italic>x</italic> film that exhibit room‐temperature ferromagnetism via a heat treatment of metallic Hf foil at 1673 K for 10 h under an oxygen partial pressure of 1.0 × 10−4 atm. The sample, which exhibits ∼50% transmission of visible light, demonstrates room‐temperature ferromagnetism, with saturation and residual magnetizations of ∼0.05 emu/g and ∼0.005 emu/g, respectively. The HfO2−<italic>x</italic> film comprises columnar grains several hundred nanometers wide and several micrometers long. High‐angle annular dark‐field scanning electron microscopy observations indicated that the tetragonal HfO2 structure was distributed in nanodomains within the monoclinic HfO2 grains; that is, the films exhibited a hybridized microstructure. The tetragonal HfO2 structure would be mainly due to the introduction of oxygen deficiencies, which led to the room‐temperature ferromagnetism. [ABSTRACT FROM AUTHOR]