Titanium <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>3</mml:mn><mml:mi>d</mml:mi></mml:math> ferromagnetism with perpendicular anisotropy in defective anatase
Markus Stiller, Alpha T. N’Diaye, Hendrik Ohldag, J. Barzola‐Quiquia, P. Esquinazi, Thomas Amelal, Carsten Bundesmann, D. Spemann, Martin Trautmann, A. Chassé, Hichem Ben Hamed, Waheed A. Adeagbo, W. Hergert
Abstract
This work focuses on the generation of ferromagnetism at the surface of anatase ${\mathrm{TiO}}_{2}$ films by low-energy ion irradiation. Controlled ${\mathrm{Ar}}^{+}$-ion irradiation resulted in a thin $(\ensuremath{\sim}10)$ 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 $\ensuremath{\sim}1\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{m}$ width and several $\ensuremath{\mu}\mathrm{m}$ length can be easily prepared.