External magnetic field dependent light transmission and scattered speckle pattern in a magnetically polarizable oil-in-water nanoemulsion

We study the magnetic field dependent light transmission and scattered speckle pattern in a magnetically polarizable oil-in-water emulsion of droplet diameter ~220 nm, where the direction of propagation of light is parallel to the direction of the external magnetic field. Up to a magnetic field of 50 Gauss, the nanoemulsion remains opaque due to intense Mie scattering. Above 50 Gauss, the transmitted light intensity increases with external magnetic field up to a critical field (BC). Further increase in the magnetic field leads to a reduction in the transmitted intensity. The BC shifts to a lower magnetic field with increasing volume fraction (ϕ) and follows a power law dependence with ϕ, indicating a disorder-order transition. The scattered light intensity at the lobe part is found to increase with external magnetic field. The analysis of the lobe part reveals that the speckle contrast increases with external magnetic field due to the coarsening of the linear chain-like aggregates formed along the direction of the external magnetic field. The angular speckle correlation coefficient is found to be symmetrical on either side of the transmitted bright spot and decays exponentially with measurement angles.