  Magneto-ionic control of magnetic properties through ionic migration has
shown promise in enabling new functionalities in energy-efficient spintronic
devices. In this work, we demonstrate the effect of helium ion irradiation and
oxygen implantation on magneto-ionically induced exchange bias effect in
Gd/Ni$_{0.33}$Co$_{0.67}$O heterostructures. Irradiation using $He^+$ leads to
an expansion of the Ni$_{0.33}$Co$_{0.67}$O lattice due to strain relaxation.
At low He+ fluence ($\leq$ 2$\times$10$^{14}$ ions cm$^{-2}$), the
redox-induced interfacial magnetic moment initially increases, owing to
enhanced oxygen migration. At higher fluence, the exchange bias is suppressed
due to reduction of pinned uncompensated interfacial Ni$_{0.33}$Co$_{0.67}$O
spins. For oxygen implanted samples, an initial lattice expansion below a dose
of 5$\times$10$^{15}$ cm$^{-2}$ is subsequently dominated at higher dose by a
lattice contraction and phase segregation into NiO and CoO-rich phases, which
in turn alters the exchange bias. These results highlight the possibility of
ion irradiation and implantation as an effective means to tailor magneto-ionic
effects.
