Time dependence of light transmission in nanoparticle ferrofluids

In this work, the time dependence of light transmission (T) through magnetic fluid is measured for a period of 600 s at different applied magnetic fields and at different fluid concentrations. The magnetic fluid consists of Fe3O4 nanoparticles with an average diameter of 36 nm. The data show that after the field is switched on, the light transmission increases monotonically with time for the first 10 s. After that the light transmission is observed to decrease with time. The time variation of light transmission in this system is explained in the frame of two relaxation regimes, first involves clusters formation which is responsible for the increase in T with time, and second involves clusters merging which is responsible for the decrease in T with time.