Proton dynamics in ultrathin GdO𝑥�H𝑦� films for magneto-ionics

Abstract

Dynamic tuning of materials properties with simple voltage control is desirable for a variety of applications, from magnetic memory, to neuromorphic computing, to solid state pixels and optical circuit components. Metal oxides can conduct ionic current, allowing their properties and those of adjacent materials to be controlled through voltage control of ion transport and electrochemical reactions. This thesis focuses on protonic defects in gadolinium oxide and gadolinium hydroxide (GdOxHy). Protons are mobile in this oxide at room temperature, and hydrogen incorporation can control a variety of materials properties, making these devices a promising platform for thin film solid state ionic devices with very simple and robust architectures. However, the proton transport and hydrogen storage properties of GdOxHy are not sufficiently well understood to determine the limits and optimal operation conditions for this material platform. Additionally, the mixed ionic and electronic conductivity of the material poses challenges for measuring these properties. This thesis sheds light on proton dynamics in nanoscale GdOxHy films in order to understand proton conductivity and hydrogen storage. The work investigates the effects of hydration and gating on the structure of GdOxHy films and devices, measures the devices' electrical and electrochemical properties, and focuses on applications in magneto-ionics, where voltage control of protons is used to toggle the magnetic properties of a ferromagnetic or ferrimagnetic layer.