Study of magneto-optical effects in γ-Fe2O3/ZnFe2O4 nanoparticle ferrofluids, using circularly polarized light

Abstract

When circularly polarized light travels through a ferrofluid film in the presence of an applied magnetic field, the transmitted light will behave as elliptically polarized light, because of magnetic birefringence and dichroism. The angular distribution of the relative intensity of the transmitted light can be obtained using a polarizer, so that the ratio of both the long and short axes—as well as the orientation angle of the ellipse, corresponding to the direction of the applied magnetic field—can be determined, and whether the ferrofluids samples are stable during the measurement can be directly judged from the shape of the distribution curves. Thus, the ratio of the amplitudes Ax/Ay and the added phase difference Δτ can be resolved in the elliptically polarized light, and information on both the magnetic birefringence Δn and the dichroism Δk can be deduced for the ferrofluid sample. From the orientation angles of both right-handed and left-handed elliptically polarized transmitted light, the direction of the applied magnetic field can be accurately determined. Using circularly polarized light, the magnetic birefringence and dichroism of pure γ-Fe2O3 ferrofluids and γ-Fe2O3/ZnFe2O4 binary ferrofluids were studied. For the binary ferrofluids, a modulating effect on the magnetic birefringence and dichroism was revealed.