Forced Rayleigh Experiment in a Magnetic Fluid

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Abstract
A spatial modulation of colloidal concentration of nanoscopic magnetic particles is written in a ferrofluid solution inside the fringes of a forced Rayleigh scattering device. The relaxation time of this transient grating is inversely proportional to the square of the characteristic wave vector and thus to the cooperative diffusion coefficient of particles. If an external magnetic field is applied in the plane of the fringes and perpendicularly to these ones, the experimental diffusion coefficient increases, due to local magnetic field gradients in the spatially inhomogeneous magnetic medium.