Hydroxide-based Magneto-ionics*

Recently, magneto-ionics has attracted a lot of interests where controlled motion of ions, e.g., under an electric field, is employed to modify metal/oxide interfaces and their magnetic responses in a reversible and non-volatile fashion. Despite the promising initial oxygen-based magneto-ionic systems, it has been demonstrated that hydrogen-based system showed better performance.
In this work, we aim to study the magneto-ionic effects in cobalt hydroxide (Co(OH)₂) / gadolinium (Gd) heterostructures. In contrast to other works, in our system both O^2- and H⁺ are contained in the initial sample. Cobalt hydroxide films are grown by electrochemical methods from a cobalt nitrate electrolyte and confirmed by x-ray diffraction. Magnetometry results showed the paramagnetic character of the sample in the as-grown state. However, after the cobalt hydroxide film is sputter-coated with a Gd layer, a clear magnetic hysteresis loop arises. Since the Tc of Gd is 292 K, the observed magnetism arises solely from the spontaneous reduction of Co(OH)₂ to Co and the formation of Gd(OH)_x. Finally, we have also demonstrated that the magnetic moment can be tailored with electric fields.