Magnetic properties and magneto-birefringence of magnetic fluids
Institute for Complex Fluids, "Politehnica'' University of
Timisoara, Bd. Mihai Viteazul 1, Timisoara 1900, Romania
West University of Timisoara, Faculty of Physics, Bd. V. Parvan 4, Timisoara 1900, Romania
Received 18 July 1999 and Received in final form 13 January 2000
Static magnetic properties of a large variety of magnetic fluids with magnetite particles is studied. A qualitative study of magnetization curves was performed to establish the influence of interactions or the presence of agglomerations in each sample. Improved equations for magneto-granulometric analysis, for ideal ferrofluids, were proposed. Better results for the mean magnetic diameter than in the case of using the known equations were obtained. A quantitative study using several models for ideal and interacting particles was performed to select the best method and dimensional distribution function for magneto-granulometric analysis as well as for accurately determining macroscopic quantities of samples (initial susceptibility, saturation magnetization, particle number density or magnetic volume fraction) and properties of nanoparticles (mean magnetic diameter, thickness of the nonmagnetic layer and particle distribution). A new model for magneto-birefringence was proposed and discussed as well as applied for diluted and concentrated ferrofluids. The Langevin behaviour of samples was investigated and compared with the investigation based on magnetic properties. Nanoparticles parameters like mean "magneto-optical'' diameter, effective anisotropy constant, Shliomis diameter and the real part of the electrical permittivity of particles were accurately determined.
75.50.Mm Magnetic liquids - 75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects - 78.20.Fm Birefringence
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag