Thermal effect on the field-dependent refractive index of the magnetic fluid film

The field-dependent refractive index (nMF–H curve) of the magnetic fluid film (MFF) is measured at various temperatures to investigate the thermal effect on the refractive index. It was found, at a certain temperature, that the refractive index becomes higher under higher magnetic fields. This nMF–H curve is moved toward the region with lower nMF when the temperature is raised. Since the variation in the refractive index of the MF under external fields is due to the formation of the magnetic columns, the structural patterns are then examined to clarify the origin of the change in the nMF–H curve with the temperature. Under a given field strength, the particles of columns are dispersed into the liquid carrier at a higher temperature. This depresses the phase separation in the MFF under fields, and in turn, reduces the refractive index of the MFF. The observed results also reveal that the temperature exhibits a compensation effect on the refractive index of the MFF with respect to the magnetic field.