Profiles of oxygen and titanium point defects in ferromagnetic TiO2 films

0584888 - ÚFM 2025 RIV GB eng J - Journal Article
Nhu, T. Q. - Friák, Martin - Miháliková, Ivana - Kiaba, M. - Hong, N. H.
Profiles of oxygen and titanium point defects in ferromagnetic TiO2 films.
Journal of Physics D-Applied Physics. Roč. 57, č. 26 (2024), č. článku 265302. ISSN 0022-3727. E-ISSN 1361-6463
Research Infrastructure: CzechNanoLab - 90110
Institutional support: RVO:68081723
Keywords : vacancies * defects * ferromagnetic * DMSO * spintronics
OECD category: Condensed matter physics (including formerly solid state physics, supercond.)
Impact factor: 3.4, year: 2022
Method of publishing: Open access
https://iopscience.iop.org/article/10.1088/1361-6463/ad3767

Experimentally it is shown that without any oxygen manipulation for TiO2, a strong room
temperature ferromagnetism could be expected only in ultra-thin films, with the ideal thickness
below 100 nm. Both bulks and nano-powders of TiO2 are diamagnetic, indicating that the
surface and its nano-sublayers play very important roles in tailoring the magnetic properties in
this type of compound. To shed a new light on the defect-related magnetism in the typical case
of anatase TiO2 surfaces, we have performed a series of quantum-mechanical calculations for
TiO2 slabs containing Ti or O vacancies in different distances from the (001) surface. The
lowest formation energies were obtained for the Ti vacancies in the first sub-surface layer and
the O vacancies within the surface. The computed magnetic states reflect complicated structural
relaxations of atoms influenced by both the surface and vacant atomic positions. O atoms cannot
contribute much to magnetic moment when Ti vacancies are isolated and far from the surface.
Ti vacancies in TiO2 are only metastable. The formation energy of Ti interstitials is lower than
for Ti vacancies since high-temperature annealing, especially with a lot of O2 available that
would fill up O-related defects, and as a result, eliminate most of Ti vacancies. Lower
temperatures, less O2, and shorter exposure times may enable not only partial elimination of Ti
vacancies but also can facilitate their diffusion into different states of aggregations. In the
ferromagnetic films (i.e. thin films below 100 nm), it looks like that the O atoms are located
closer to the Ti vacancies.
Permanent Link: https://hdl.handle.net/11104/0352728