Control of Oxygen Vacancy Ordering in Brownmillerite Thin Films via Ionic Liquid Gating

Abstract

Oxygen defects and their atomic arrangements play a significant role in the physical properties of many transition metal oxides. The exemplary perovskite SrCoO_3-δ (<i>P-</i>SCO) is metallic and ferromagnetic. However, its daughter phase, the brownmillerite SrCoO_2.5 (<i>BM-</i>SCO), is insulating and an antiferromagnet. Moreover, <i>BM-</i>SCO exhibits oxygen vacancy channels (OVCs) that in thin films can be oriented either horizontally (<i>H</i>-SCO) or vertically (<i>V</i>-SCO) to the film's surface. To date, the orientation of these OVCs has been manipulated by control of the thin film deposition parameters or by using a substrate-induced strain. Here, we present a method to electrically control the OVC ordering in thin layers via ionic liquid gating (ILG). We show that <i>H</i>-SCO (antiferromagnetic insulator, AFI) can be converted to <i>P</i>-SCO (ferromagnetic metal, FM) and subsequently to <i>V</i>-SCO (AFI) by the insertion and subtraction of oxygen throughout thick films via ILG. Moreover, these processes are independent of substrate-induced strain which favors formation of <i>H</i>-SCO in the as-deposited film. The electric-field control of the OVC channels is a path toward the creation of oxitronic devices.