Room-temperature ferromagnetism in un-doped ZrO2 thin films

Room-temperature ferromagnetism was observed in un-doped ZrO2 thin films prepared by pulsed electron beam deposition on silicon substrates. In the obtained films, monoclinic and tetragonal phases were both stabilized, with a ratio depending on the oxygen partial pressure during deposition. The ferromagnetism was positively related to the tetragonal phase content, and had a positive linear relationship with the photoluminescence (PL) intensity of emission centred at ~420 nm related to the singly ionized oxygen vacancies, as revealed further by the PL analysis. This study suggested that the oxygen vacancies, which stabilized the tetragonal phase at room-temperature, should be the origin of ferromagnetism in un-doped ZrO2 films.