Metastable Ordered Mesoporous h ‐LuFeO ₃ Thin Films Prepared by Soft‐Templating: Optical, Electronic, and Magnetic Properties

ABSTRACT A sol–gel‐based soft‐templating strategy for the synthesis of a hexagonal rare‐earth orthoferrite and characterization of its structural, optical, electronic, and magnetic properties are reported. Specifically, the work aims to show that amphiphilic block copolymers as structure‐directing agents (SDAs) are suitable for the production of metastable h ‐LuFeO ₃ , a phase that is not observed without SDA. The ability of the polymer SDA used herein to self‐organize into superstructures while remaining compatible with inorganic building blocks, known as the evaporation‐induced self‐assembly process (EISA), resulted in a honeycomb‐like network of open pores. In contrast to conventional epitaxy, it is demonstrated that the h ‐LuFeO ₃ can be readily deposited as polycrystalline thin films on both silicon and quartz substrates by facile dip coating. The formation mechanism of the mesoporous material during calcination in air is investigated using various physicochemical characterization techniques. This revealed that certain reaction intermediates are produced that promote the formation of the hexagonal phase. Density functional theory calculations support the experimentally derived properties and further provide information on the electronic band structure. Overall, this study demonstrates a novel synthetic approach for producing ordered mesoporous and ferromagnetic LuFeO ₃ thin films in the hexagonal rather than the orthorhombic phase due to the presence of a polymer SDA during synthesis.