Enhancement of the field modulation of light transmission through films of binary ferrofluids

CoFe2O4 nanoparticles are ferrimagnetic and p-MgFe2O4 nanoparticles are paramagnetic. Binary ferrofluids can be synthesized by mixing CoFe2O4 ferrofluids and p-MgFe2O4 fluids in such a way that the magnetic interaction of the CoFe2O4 particles is large enough to form field-induced chainlike aggregates. The field modulation of light transmission through films of CoFe{2}O{4}-p-MgFe2O4 binary ferrofluids with different values of applied magnetic field is compared with pure CoFe2O4 ferrofluids. The experimental results revealed that the light transmission coefficient of binary ferrofluids can be more intensely modulated by an external magnetic field than pure CoFe2O4 ferrofluids. These show that in the binary ferrofluids, the field-induced structure mainly arises from the CoFe2O4 nanoparticle system and the p-MgFe2O4 nanoparticles introduce a nonlinear modulation effect, even though the microstructure of p-MgFe2O4 fluids is not affected by an applied magnetic field. Using a model of magnetic bidispersal, the enhanced field modulation of the light transmission through binary ferrofluids is explained by the coupling of geometric shadowing effects from both the CoFe2O4 and p-MgFe2O4 particle systems.