Films*

Electrolyte gating has proven remarkably effective in controlling electronic, magnetic, and optical materials properties. Both electrostatic and electrochemical mechanisms occur [1], one example of the latter being the voltage-driven perovskite (P) to brownmillerite (BM) transition found in SrCoO_3-d [2], which realizes a ferromagnetic metal/antiferromagnetic insulator transition. In this work, we provide the first complete doping- and strain-dependent study of the ion-gel-gating-induced P to BM transition over the entire La_1-xSr_xCoO_3-δ phase diagram, via transport, magnetometry, and operando synchrotron X-ray diffraction. The electrically-actuated P to BM transition is found to occur over a wide x range, modulating the Curie temperature over ~220 K. Most significantly, the variation in threshold voltage with x and strain point to electrochemical activity controlled by the Co⁴⁺/Co³⁺ ratio, interpreted in terms of trends in thermodynamic rather than kinetic (i.e., oxygen vacancy diffusion) parameters. These results provide global insight into the electrochemical control of this model oxide.
1. Leighton, Nat. Mat. 18, 13 (2018).
2. Lu et al., Nature 546, 124 (2017).
3. Chaturvedi et al., in prep.