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We report the synthesis of lyotropic ferronematics with a content of magnetic nanoparticles (~6 nm) up to 1 vol.%. In the ferrodiscotic phase we observe a magnetic Frederiks transition with critical fields about two orders of magnitude lower than that for an undoped lyotropic system. A model accounting for the magnetic polarization behavior of the studied ferronematics is presented.

Magnetodynamics of ferrofluid γ-Fe2O3 nanoparticles is studied by Quasi-Elastic Neutron Scattering between 10 K and 250 K in the frequency range 1010–1012 Hz. We probe independently the precession of the core magnetic moment and surface spins fluctuations observed in a dissipative regime. These fluctuations slow down at low temperature leading to a frozen disorder of the surface layer.

A new theoretical approach to the dynamic field-induced birefringence in magnetic fluids is presented. On equal basis it takes into account both internal (magnetic) and external (mechanical) orientation relaxations of the particles. Besides uniting several former approximate models, already tested experimentally, it covers a variety of intermediate cases which have been never addressed before.