Titanium 3d ferromagnetism with perpendicular anisotropy in defective anatase

Phys. Rev. B 101, 014412 (2020)

M. Stiller, A.T. N’Diaye, H. Ohldag, J. Barzola-Quiquia, P.D. Esquinazi, T. Amelal, C. Bundesmann, D. Spemann, M. Trautmann, A. Chassé, H.B. Hamed, W.A. Adeagbo, and W. Hergert

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 ∼1 μm width and several μm length can be easily prepared.