Effects of Birefringence and Dichroism in Magnetic Fluids with Different Degrees of Aggregative Stability

Spectra of optical effects of dichroism and birefringence are investigated in magnetic fluids like magnetite in kerosene with the average particle sizes of 6.7 and 13.7 nm. Substantial differences in the magnitude of the effects and in their spectral behavior are found that stem from the formation of aggregates in a sample with larger particles. The presence of particle aggregates appreciably changes the optical properties of the system. The effects are interpreted on the basis of the single-particle orientation model with allowance for the superparamagnetism of magnetite nanoparticles.