Titanium 3d ferromagnetism with perpendicular anisotropy in defective anatase

• Published in: Physical review. B 2020-01, Vol.101 (1), p.1
• Main Authors: Stiller, Markus, N'Diaye, Alpha T, Ohldag, Hendrik, Barzola-Quiquia, José, Esquinazi, Pablo D, Amelal, Thomas, Bundesmann, Carsten, Spemann, Daniel, Trautmann, Martin, Chassé, Angelika, Hamed, Hichem Ben, Adeagbo, Waheed A, Hergert, Wolfram
• Format: Article
• Language: English
• Subjects: Anatase; Anisotropy; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Defects; Density functional calculations; Density functional theory; Dichroism; Domain walls; Ferromagnetism; Ion irradiation; Irradiation effects; Magnetic anisotropy; Magnetic domains; Magnetic fields; Magnetism; Magnetization; Remanence; Room temperature; Superconducting quantum interference devices; Surface layers; Titanium; Titanium dioxide; X-ray magnetic circular dichroism
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.101.014412

This work focuses on the generation of ferromagnetism at the surface of anatase TiO2 films by low-energy ion irradiation. Controlled Ar+-ion irradiation resulted in a thin (∼10) nm ferromagnetic surface layer. The intrinsic origin and robustness of the magnetic order has been characterized by x-ray magnetic circular dichroism at room temperature revealing that a Ti band is spin-polarized. These results, together with density functional theory calculations, indicate that Ti vacancy-interstitial pairs are responsible for the magnetic order. Superconducting quantum interference device measurements show the existence of a perpendicular magnetic anisotropy and a low remanent magnetization. Magnetic force microscopy reveals that this low remanence is due to oppositely aligned magnetic domains with magnetization vectors normal to the main surface. The weak domain-wall pinning, the magnetic anisotropy, together with the simplicity of the preparation method, open up interesting possibilities for future applications. As an example, single domain patterns of ∼1μm width and several μm length can be easily prepared.