  Voltage control of magnetism through electric field-induced oxygen motion
(magneto-ionics) could represent a significant breakthrough in the pursuit for
new strategies to enhance energy efficiency in a large variety of magnetic
devices, such as magnetic micro-electro-mechanical systems (MEMS), magnetic
logics, spin electronics, or neuromorphic computing, i.e., envisaging ultra-low
power emulation of the biological synapse. Boosting the induced changes in
magnetization, magneto-ionic motion and cyclability (endurance) continue to be
key challenges to turn magneto-ionic phenomena into real applications. Here, we
demonstrate that, without degrading cyclability, room temperature magneto-ionic
motion in electrolyte-gated paramagnetic and fairly thick (> 100 nm) Co3O4
films largely depends on the configuration used to apply the electric field. In
particular, magneto-ionic effects are significantly increased both in terms of
generated magnetization (6 times larger: from 118.5 to 699.2 emu cm-3) and
speed (35 times faster: from 33.1 to 1170.8 emu cm-3 h-1) if the electric field
is applied across a conducting buffer layer (grown underneath the Co3O4 films),
instead of directly contacting Co3O4. This is attributed to a greater
uniformity and strength of the applied electric field when using the conducting
layer. These results may trigger the use of oxygen magneto-ionics into
promising new technologies, such as magnetic MEMS or brain-inspired computing,
which require endurance and moderate speeds of operation.
