Magnetism of Ultrathin TiO₂ Films Prepared by Atomic Layer Deposition

The discovery of room-temperature ferromagnetism (FM) in pristine TiO2 films has sparked intense debate regarding its origin, particularly in the absence of conventional magnetic dopants. Herein, for the first time, the FM of ultrathin TiO2 films grown on LaAlO3 (LAO) substrates by Atomic Layer Deposition (ALD) is investigated, yielding TiO2 thicknesses of 1, 5, and 10 nm. The findings reveal a striking thickness-dependent magnetic response, where the 5 nm films exhibit the highest ferromagnetic response, attributed to defect-driven mechanisms. Structural and spectroscopic analyses, complemented by quantum mechanical calculations, highlight the critical role of oxygen vacancies and/or defects, as well as the interface with LAO substrates, in modulating the observed FM. Notably, this work demonstrates that the ferromagnetic behavior is confined to the in-plane direction, reinforcing the role of surface and interface effects. These insights establish that defects play a key role in tuning the electronic and magnetic properties of ultrathin TiO2 films, paving the way for potential applications in next-generation magnetic devices.