  Magneto-ionics has emerged as a promising approach to manipulate magnetic
properties, not only by drastically reducing power consumption associated with
electric current based devices but also by enabling novel functionalities. To
date, magneto-ionics have been mostly explored in oxygen-based systems, while
there is a surge of interests in alternative ionic systems. Here we demonstrate
highly effective hydroxide-based magneto-ionics in electrodeposited
${\alpha}$-Co(OH)$_{2}$ films. The ${\alpha}$-Co(OH)$_{2}$, which is a room
temperature paramagnet, is switched to ferromagnetic after electrolyte gating
with a negative voltage. The system is fully, magnetically reversible upon
positive voltage application. The origin of the reversible
paramagnetic-to-ferromagnetic transition is attributed to the ionic diffusion
of hydroxyl groups, promoting the formation of metallic cobalt ferromagnetic
regions. Our findings demonstrate one of the lowest turn-on voltages reported
for propylene carbonate gated experiments. By tuning the voltage magnitude and
sample area we demonstrate that the speed of the induced ionic effect can be
drastically enhanced.
