Room temperature ferromagnetism in un-doped amorphous HfO₂ nano-helix arrays

Amorphous HfO₂ nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO₂ nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO₂, it also suggests a possible way to alter the intrinsic defects in amorphous HfO₂.