Magnetic properties and magneto-birefringence of magnetic fluids

Static magnetic properties of a large variety of magnetic fluids with magne tite particles is studied. A qualitative study of magnetization curves was performed to establish the influence of interactions or the presence of agg lomerations in each sample. Improved equations for magneto-granulometric an alysis, for ideal ferrofluids, were proposed. Better results for the mean m agnetic diameter than in the case of using the known equations were obtaine d, A quantitative study using several models for ideal and interacting part icles was performed to select the best method and dimensional distribution function for magneto-granulometric analysis as well as for accurately deter mining macroscopic quantities of samples (initial susceptibility, saturatio n magnetization, particle number density or magnetic volume fraction) and p roperties of nanoparticles (mean magnetic diameter, thickness of the nonmag netic layer and particle distribution). A new model for magneto-birefringen ce was proposed and discussed as well as applied for diluted and concentrat ed ferrofluids. The Langevin behaviour of samples was investigated and comp ared with the investigation based on magnetic properties. Nanoparticles par ameters like mean "magneto-optical" diameter, effective anisotropy constant , Shliomis diameter and the real part of the electrical permittivity of par ticles were accurately determined.