Field-induced aggregates in a bilayer ferrofluid characterized by ultrasound spectroscopy.

This paper presents dynamic changes in ferrofluid properties during a magnetic field sweep. The study reported was performed on a ferrofluid with a double layer of surfactant used to prevent aggregation of particles. The ferrofluid parameters (the radius and volume of the cluster, the elastic force constant) were studied by the ultrasound wave absorption method as a function of the dynamically changing magnetic field. During the application of the magnetic field from 0 to 100 kA m(-1) the structure in the ferrofluid evolves and become anisotropic. The magnetic field was found to stimulate formation of micrometre clusters and exponential increase in the elastic force constant.