Microstructures and room temperature ferromagnetism of ordered porous ZrO₂ thin films sputter deposited onto porous anodic alumina substrates

Ordered porous ZrO₂ films with pore diameters in the 5–45 nm range have been prepared on porous anodic alumina substrates using DC-reactive magnetron sputtering of pure Zr targets. A saturation magnetization (M_S) value as high as 119 emu/cm³ was obtained for the ZrO₂ film with pores of 45 nm in diameter when the external field was perpendicular to the film surface. The significant out-of-plane saturation magnetization is associated with the porous structure of the film. Experimental and theoretical results showed that the origin of the room temperature ferromagnetism (RTFM) is closely related to the ordered porous structure and the single charged oxygen vacancies of the films. These findings suggest that porous ZrO₂ films are promising to be applied to the spin electronic devices. - Highlights: • Porous ZrO₂ films with pore diameters in the 5–45 nm range were deposited on porous anodic alumina substrates. • Significant ferromagnetism has been observed in porous ZrO₂ films (119 emu/cm³). • The ferromagnetism along the out-of-plane direction is much larger than that along the in-plane direction. • The single charged oxygen vacancies and the unique porous structure of the films are responsible for the large ferromagnetism.