TEMPERATURE AND CONCENTRATION-DEPENDENCE OF MAGNETIC BIREFRINGENCE OF MAGNETIC FLUIDS

It was found experimentally that the magnetic birefringence of magnetic fluid thin films obeys a Curie-Weiss like law for all kinds of magnetic fluids except for a water-based one. The birefringence can be described by θ(T, H) = θaf(H)/[T-Ta+f(H)], where θ(T, H), H and T are the phase difference, the applied field and the temperature of the film, respectively, and θa is a positive constant. Ta and f(H) are also found to be expressed empirically by Ta=T0 + κ ln c, f(H)=1-exp[-α(c)H], respectively, where c is a volume fraction of the colloidal particles, T0, κ are positive constants and α(c) is a function of c. Taking the empirical expression of θ into consideration, the free energy of the magnetic fluid is discussed using Landau's phase transition theory. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.