The influence of aggregates and relative permeability on the magnetic birefringence in ionic magnetic fluids

The static magnetic birefringence (SMB) of nickel-ferrite ionic magnetic fl uid was investigated within the oscillating dipole-interaction anisotropy c oncept proposed by Xu and Ridler [J. Appl. Phys. 82, 326 (1997)]. The model was extended to include the magnetic texture of particle agglomerates and the field dependence of the magnetic permeability. The SMB data of samples subjected or not to a magnetic aging process and presenting particle concen tration in the range of 2x10(16) to 8x10(16) particle/cm(3) were successful ly described. The particle size distribution obtained from the fit of the S MB data was discussed in comparison with the data obtained from transmissio n electron microscopy. (C) 2001 American Institute of Physics.