Hydration of gadolinium oxide (GdOx) and its effect on voltage-induced Co oxidation in a Pt/Co/GdOx/Au heterostructure

Magneto-ionic control of magnetism has garnered great interest in recent years due to the large magnetic changes that can be induced using a relatively small voltage. One model structure for this is Pt/Co/GdO_x/Au , where Co is the magnetic layer and GdO_x is the ionic conductor, with the magnetic properties dependent on the oxidation state of Co. While this structure is commonly used, there is limited understanding of the effect of GdO_x properties on voltage-induced magnetic changes. In this work, we show that hydration of Gd₂O₃ to form Gd(OH)₃ is crucial for voltage-induced Co oxidation in a Pt/Co/GdO_x/Au device. By examining the rate of Co oxidation in nonhydrated and hydrated devices, we conclude that H₂O in the GdO_x layer acts as an oxidant during the voltage-induced Co oxidation process. Co oxidation through this interfacial reaction process is confirmed by in situ x-ray absorption spectroscopy.