Magnetic-field-induced optical transmittance in colloidal suspensions

Through simulation and experiment we demonstrate that when a magnetic field is applied to a suspension of magnetic particles, the optical attenuation length along the direction of the field increases dramatically, due to the formation of chainlike structures that allow the transmission of light betw een the strongly absorbing particles. This phenomenon is interesting for tw o reasons; first, there might be practical applications for this effect, su ch as optical-fiber-based magnetic field sensors, and second, measuring the time evolution of the optical attenuation length enables us to determine t he kinetics of structure formation, which can be compared to the prediction s of simulation and theory. In agreement with both simulation and theory, t he optical attenuation length increases as a power of time, but much less l ight is actually transmitted than expected, especially at higher particle c oncentrations. We conclude that particle roughness, which is not included i n either theory or simulation, plays a significant role in structural devel opment, by pinning structures into local minima. [S1063-651X(99)05405-7].