In Situ Tuning of Magnetization Via Double Layer Charging and Topotactic Li Insertion in Polymer-Templated Mesostructured Thin Films

Abstract

Mesostructured mixed-metal oxide thin films have received much attention in recent years, as they have great potential for future device applications. Advances in polymer templating over the past years have enabled the preparation of a variety of important materials in the form of thin films. However, despite the progress made, complex metal oxides (other than binary systems) often exhibit an ill-defined nanoscale structure after thermally-induced crystallization and removal of the porogen, mainly for stability reasons. Here, we describe the self-assembling synthesis of large-pore mesoporous mixed-metal oxides, with special emphasis on La1–x Ca x MnO3 (LCMO) and alpha-LiFe5O8 (LFO). Electron microscopy, GISAXS, XRD, XPS, TOF-SIMS, and RBS all show that these materials can be templated to produce high quality thin films that are phase pure and thermally stable to over 600 °C. For LCMO, we demonstrate that the surface charge carrier density can be tuned by double layer charging using an ionic liquid electrolyte.[1] Peak-to-peak magnetization modulation values of up to 10% have been achieved, (to our knowledge) the highest thus far reported for electrolyte-gated mixed-valence manganese oxides. Furthermore, we demonstrate that the topotactic Li insertion into LFO allows for the intriguing possibility of controlling the r.t. bulk magnetic state in a highly reversible manner. Overall, both approaches are promising and should be applicable to other magnetic nanomaterials. [1] C. Reitz, P. M. Leufke, R. Schneider, H. Hahn, and T. Brezesinski, Chem. Mater. 26, 5745 (2014).