Magnetic response of photonic crystals based on nucleating agents of binuclear complexes

Abstract

The solvothermal reduction method, utilizing a single FeCl₃ as the iron source, is considered to be one of the effective ways to synthesize Fe₃O₄ magnetically responsive photonic crystals (MRPCs). However, some studies have revealed that Fe₃O₄ synthesized via this method cannot form a photonic crystal structure when subjected to a magnetic field, and the underlying reason for this inconsistency remains unreported. In our investigation, we have discovered that the presence of trace amounts of Fe²⁺ in the FeCl₃ reagent is essential for successfully producing Fe₃O₄ MRPCs through this method. Moreover, the size, saturated magnetization value, and photonic tuning range of MRPCs can be controlled by adjusting the Fe²⁺ content. By analyzing the structure of the precursor formed during the reaction, we identified the formation of a binuclear iron structure in the precursor. This binuclear iron structure plays a pivotal role in the formation of Fe₃O₄ MRPCs. Based on these findings, we propose a new perspective that the binuclear iron complex serves as a nucleating agent for the formation of Fe₃O₄ MRPCs. The proposed view of nucleation could have considerable effect on the preparation of mixed-valence metal oxides through the solvothermal reduction route, and the results provide a facile method to modulate MRPCs, which is important for future applications in sensors, color displays, and gratings.