  Materials with a coexistence of magnetic and ferroelectric order (i.e.,
multiferroics) provide an efficient route for the control of magnetism by
electric fields. Unfortunately, a long-sought room temperature multiferroic
with strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic)
orderings is still lacking. Here, we propose that hydrogen intercalation in
antiferromagnetic transition metal oxides is a promising way to realize
multiferroics with strong magnetoelectric coupling. Taking brownmillerite
SrCoO2.5 as an example, we show that hydrogen intercalated SrCoO2.5 displays
strong ferrimagnetism and large electric polarization in which the hydroxide
acts as a new knob to simultaneously control the magnetization and polarization
at room temperature. We expect that ion intercalation will become a general way
to design magnetoelectric and spintronic functional materials.
