Manipulate the Electronic and Magnetic States in NiCo<sub>2</sub> O<sub>4</sub> Films through Electric-Field-Induced Protonation at Elevated Temperature.

Wang, Meng; Sui, Xuelei; Wang, Yujia; Juan, Yung-Hsiang; Lyu, Yingjie; Peng, Huining; Huang, Tongtong; Shen, Shengchun et al. · Adv Mater · 2019

basic_science · Level V

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Abstract

Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO<sub>2.5</sub> , VO<sub>2</sub> , WO<sub>3</sub> , etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo<sub>2</sub> O<sub>4</sub> , an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo<sub>2</sub> O<sub>4</sub> from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.