d0 ferromagnetic display of zirconia nanocrystallites and the impact of gold doping on their structural, optical, and magnetic properties

[Formula: see text] ferromagnetism is currently under extensive investigation as an alternative to transition metal-doped dilute magnetic semiconductors in the continuously evolving field of spintronics and optoelectronic applications. The literature contains numerous conflicting sources regarding its origin, specifically in materials such as oxides, making it a subject of ongoing controversy. This work mainly centers on the interplay among gold doping, oxygen concentration, and resulting changes in the structural, optical, and magnetic characteristics, with a specific focus on [Formula: see text] ferromagnetism and room temperature ferromagnetism in sol–gel synthesized zirconia nanocrystals. The powder samples crystallized in a mixed monoclinic-tetragonal phase. The weak absorbance band around 280[Formula: see text]nm and the O-1s peak in X-ray photoelectron spectroscopy provide insights into the metastable tetragonal phase’s stability, attributed to oxygen vacancies. The bandgap slightly increases from 4.6[Formula: see text]eV to 5.0[Formula: see text]eV due to the transformation from a tetragonal to a monoclinic phase. Magnetic studies reveal room-temperature ferromagnetism induced by oxygen vacancies in undoped zirconia, while a shift from ferromagnetic to paramagnetic behavior occurs in gold-infused zirconia samples.