  Electrical control of oxygen off-stoichiometry of transition-metal oxides at
room temperature is a desired strategy to simultaneously switch the electrical
conductance and magnetism of the device. Although the use of the
electrochemical redox reaction of transition-metal oxides is the most
reasonable way to achieve the aforementioned switch, such a device has not been
realized because of the lack of a leakage-free liquid electrolyte. Here, we
demonstrate an electromagnetic device that can reversibly switch a
transition-metal oxide from an insulator/non-magnet to a metal/magnet (Tc=275
K) using a newly developed 'leakage-free electrolyte', incorporated in an
amorphous NaTaO3 nanopillar array film. Reversible switching occurs
electrically, obeying Faraday's laws of electrolysis, under a DC voltage of
+(-)3 V within 2-3 s at RT. The present electromagnetic device does not have
the drawback of liquid leakage, and the leakage-free electrolyte provides a
novel design concept for practical electromagnetic devices using
transition-metal oxides.
