The magnetic fluid comprises of single domain magnetite nanoparticles, suspended in water and stabilized using dodecanoic acid has been studied here. The optical properties of two different magnetic volume fractions, i.e. 8.2 ×10^(-4), and 4.92 × 10^(-3) and coded as FN30 and F30 respectively have been selected for the present study. Interestingly, it is observed that the magnetic fluid having low magnetic volume fraction, i.e. FN30, exhibits high change in magnetic field induced birefringence, which is differing from the magnetization data, which indicates that the mean magnetic moment of F30 is higher. The magnetic field induced birefringence establishes tunability, and has potential to develop as next generation optical devices.

The present study reports magnetic and optical properties of silica mediated lauric acid stabilized magnetic fluids. The tunable birefringence (Δn) and other properties are investigated as a function of (i) concentrations of silica suspension, and (ii) saturation magnetization (MS) 0.5099 kAm−1 (FN30) and 1.2855 kAm−1 (F30) of magnetite magnetic fluid (MF). The study reveals thatΔn suppresses on addition of silica in FN30, whereas enhances (up to critical concentrations of silica) in F30. The magnetic field induced chain observed in the FN30 based fluids are long, thick and scattered, while short, thin and dense chains emerges in F30 based fluid. The magnetic field induced assembly and the magnetic parameters correlates with the results ofΔn. The particle size analysis indicates increment of particle size on addition of silica nanoparticles. The thermogravimetry analysis confirms the direct interaction of silica nanoparticles and the lauric acid coated magnetite particles. This is the first report of direct interaction of silica—magnetite magnetic fluids, and its subsequent effect on tunable birefringence and other properties.

Aqueous magnetic nanofluid consists of superparamagnetic nanoparticles, with a typical size of 10–12 nm. On the application of a magnetic field, these nanoparticles align heterogeneously and form a chain or chain-like structure. This structure is observed using a microscope. Although many articles report such chain or microstructure formation well, the method to identify and determine chain parameters, e.g., chain length, width, and associated counts, is scarce. Similarly, interchain or successive distance is one of the critical parameters for developing magnetic nanofluid-based devices. The work describes magnetic field-induced chain parameters (MFCP) and magnetic field-induced interchain distance (MFID), a set of developed protocols in the ImageJ software to identify and determine the (i) chain length, width, and associated counts, along with (ii) successive distance of the magnetic chains in the magnetic nanofluid. This utilizes a macro file such as MFCPji.txt and MFIDji.txt for ImageJ, which can be used on microscopic images of magnetic nanofluids without applying a magnetic field. The protocol does not require specialized scientific equipment and can be carried out using open-source software ImageJ/Fiji. The examples of microstructure formations in two different magnetic fluids (A and B) are discussed. In addition, the results of the associated weighted average chain length, chain width, number of chains, and the successive chain distance are reported. The chain parameters are helpful to determine diffraction grating angles. The MFCPji and MFIDji macros have been integrated into a macro toolset that can be configured to be run on ImageJ startup. The MFCPji and MFIDji are available from the following Uniform Resource Locator (URLs): https://github.com/urveshsoni/ImageJ-Macros and https://ruchadesailab.wordpress.com/publication/