A macroscopic magneto-optical response resulting from local effects in ferronematic liquid crystals†

Abstract

This study investigates the magneto-optical response of liquid crystals (LCs) with planar anchoring in the presence of γ-Fe₂O₃ magnetic nanoparticles (MNPs). This research demonstrates the formation of novel magnetic composite chains of LCs wrapped around γ-Fe₂O₃ MNP chains within the LC matrix under an applied magnetic field. These composite chains exhibit a distinct magneto-optical response, characterized by changes in birefringence and dichroism as the magnetic field direction is altered. Based on experimental findings, a two-subsystem model and an effective volume fraction of composite chains are proposed to describe the magneto-optical behavior of the γ-Fe₂O₃ MNP-doped LCs. The first subsystem comprises the LC matrix, which retains its inherent anisotropic optical properties and does not respond to the applied magnetic field. The second subsystem consists of the magnetic composite chains, which exhibit a distinct magneto-optical response due to their rotational alignment with the magnetic field. The difference in absorbance, 2α_dd, which corresponds to dichroism, decreases with increasing magnetic field angle Θ, indicating a corresponding change in dichroism. This interplay between the two subsystems leads to the macroscopic magneto-optical response observed in the γ-Fe₂O₃ MNP-doped LCs. Due to the stability of the composite chains, the magneto-optical response is stable and can be reversed.