Phase-dependent and defect-driven d0 ferromagnetism in undoped ZrO2 thin films

Abstract

Undoped ZrO₂ thin films are prepared on 〈100〉 Si substrates by reactive DC magnetron sputtering using a Zr target. By controlling the oxygen partial pressure during the deposition process, we can successfully control the phase structure of the as-deposited film, which can be tetragonal, monoclinic or a mixture of them. A magnetic property measurement reveals that phase-dependent d⁰ ferromagnetism exists in ZrO₂ thin films. Specifically, only tetragonal ZrO₂ thin films can be room-temperature ferromagnetic. Photoluminescence measurements, X-ray photoelectron spectroscopy analyses and post thermal annealing experiments suggest the d⁰ ferromagnetism in undoped tetragonal ZrO₂ films is mainly driven by oxygen vacancies.