Multiple Magnetoionic Regimes in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi>Ta/Co</mml:mi><mml:mn>20</mml:mn></mml:msub><mml:msub><mml:mi>Fe</mml:mi><mml:mn>60</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">B</mml:mi><mml:mn>20</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mi>Hf</mml:mi><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>
Rohit Pachat, Djoudi Ourdani, Johannes W. van der Jagt, Maria‐Andromachi Syskaki, Adriano Di Pietro, Y. Roussigné, Shimpei Ono, M. S. Gabor, Mourad Chérif, Gianfranco Durin, J. Langer, M. Belmeguenai, D. Ravelosona, Liza Herrera Diez
Abstract
In ${\mathrm{Ta/(Co,Fe)B/HfO}}_{2}$ stacks, a gate voltage drives, in a nonvolatile way, the system from an underoxidized state exhibiting in-plane anisotropy (IPA) to an optimum oxidation level resulting in perpendicular anisotropy (PMA) and further into an overoxidized state with IPA. The $\mathrm{IPA}\phantom{\rule{0.1em}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{0.1em}{0ex}}\mathrm{PMA}$ regime is found to be significantly faster than the $\mathrm{PMA}\phantom{\rule{0.1em}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{0.1em}{0ex}}\mathrm{IPA}$ regime, whereas only the latter shows full reversibility under the same gate voltages. The effective damping parameter also shows a marked dependence with gate voltage in the $\mathrm{IPA}\phantom{\rule{0.1em}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{0.1em}{0ex}}\mathrm{PMA}$ regime, going from 0.029 to 0.012, and only a modest increase to 0.014 in the $\mathrm{PMA}\phantom{\rule{0.1em}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{0.1em}{0ex}}\mathrm{IPA}$ regime. The existence of two magnetoionic regimes has been linked to a difference in the chemical environment of the anchoring points of oxygen species added to underoxidized or overoxidized layers. Our results show that multiple magnetoionic regimes can exist in a single device and that their characterization is of great importance for the design of high-performance spintronics devices.