Magneto-Ionics in Annealed W/CoFeB/HfO2 Thin Films

 The magneto-ionic modulation of the Dzyaloshinskii–Moriya interaction

(DMI) and the perpendicular magnetic anisotropy (PMA), in W/CoFeB/HfO2

 stacks annealed at different temperatures and for varying annealing times,

are presented in this work. A large modulation of PMA and DMI is observed

in the systems annealed at 390 and 350 ° C, whereas no response to voltage is

observed in the as-grown samples. A strong DMI is only observed in the samples

annealed at 390 ° C for 1 h, while PMA is present for all annealing times

at temperatures of 390 and 350 ° C. Magnetic properties including domain

wall velocity improve drastically with increasing the annealing temperature

and time, while the magneto-ionic reversibility is increasingly compromised.

The changes in PMA and DMI induced by the gate voltages in the samples

annealed at 390 ° C are permanent, while partial reversibility is only observed

for the samples annealed at 350 ° C for short times. This dependence of reversibility

on post-grown annealing has been associated to the influence of crystallization

on ion mobility. These results show that a compromise between the

enhancement of the magnetic properties and the magneto-ionic performance

could be needed in systems requiring annealing to develop PMA and DMI.