Origin and applications of magnetically tunable refractive indexof magnetic fluid films

TLDR

The study investigates the feasibility of using magnetic fluid films as tunable optical devices based on their field‑dependent refractive index. The authors modeled the refractive index by accounting for column formation and liquid‑phase concentration changes in magnetic fluid films under magnetic fields, then compared the calculations with experiments. Experiments show that the refractive index of magnetic fluid films increases with magnetic field strength, with a critical field threshold, and that phase separation under the field drives this tunability.

Abstract

When an external field was applied, the refractive index of the magnetic fluid film was observed to be modulated as the field exceeded a critical strength. We found that the stronger the magnetic field, the higher the refractive index. By taking both the formation of the columns and the variation in the concentration of the liquid phase in magnetic fluid films under external magnetic fields into account, the refractive index was calculated and compared with experimental data. When we did this, we noticed a consistency that implies that the phase separation leads to the variation in the refractive index of the magnetic fluid film as the magnetic field strength is changed. With such a property as a tunable refractive index, the feasibility of using a magnetic fluid in a tunable optical device is worthy of investigation.