TEMPERATURE-DEPENDENCE OF BIREFRINGENCE AND DICHROISM IN MAGNETIC FLUIDS

Measurements of the birefringence and dichroism in Fe3O4 magnetic fluids were undertaken in the temperature range 100-320 K in magnetic fields up to 0.9 kOe. Our results show that both the birefringence and dichroism are not noticeable for temperatures below 170 K. Above 170 K there is an increase with temperature exhibiting a peak at ∼ 190 and ∼ 270 K respectively. Moreover, our results show that for temperatures above that at which the peak occurs the birefringence follows a generalized Curie-Weiss law yielding positive ordering temperatures. © 1990.