Multiple magneto-ionic regimes in Ta/Co20Fe60B20/HfO2

In Ta/(Co,Fe)B/HfO2 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 IPA→PMAregime is found to be significantly faster than the PMA→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 IPA→PMA regime, going from 0.029 to 0.012, and only a modest increase to 0.014 in the PMA→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.