TOPICAL REVIEW: Recent progress in magnetic fluid research

Investigations of the properties, the flow and the application possibilities of suspensions of magnetic nanoparticles are an extremely lively research field nowadays. In particular, the biomedical application and the investigation of the rheological properties of these so-called ferrofluids gained high importance during the last years. Within this paper particular focus will be put on recent development in the field of rheological investigations of ferrofluids and their importance for the general treatment of ferrofluids. As will be outlined, recent experimental as well as theoretical investigations have shown that the formation of structures of magnetic nanoparticles has significant influence on the magnetoviscous behaviour of ferrofluids. The dependence of this structure formation on the magnetic field strength and shear stress applied to the fluid leads to strong changes of viscosity and to the appearance of viscoelastic effects in the fluids. The new findings have led to consistent microscopic models for the viscous properties of ferrofluids and they have driven the development of a macroscopic theory predicting new effects in ferrofluid dynamics.