THE MAGNETOOPTICAL BIREFRINGENCE AND INITIAL SUSCEPTIBILITY OF VERY DILUTE MAGNETIC FLUIDS

In this paper the behaviour of birefringence and the initial susceptibility in the low concentration range (epsilon = 1.34 x 10(-5) to 0.01) have been examined for magnetite ferrofluids. Our measurements show that the initial degree of clustering does not change appreciably by diluting the sample. In low fields the birefringence results from the shape anisotropy of single particles. In the case where particle interactions are pronounced the birefringence results from the interactions within the pre-existing clusters in the sample.