Magnetic Properties of Ferrogels

This paper presents the magnetic properties of ferrogels subject to cyclic magnetic fields. Ferrogels are compliant materials composed of a nonmagnetic, flexible matrix with a micro- or nano-sized magnetic powder filler. In this paper a poly-vinyl-alcohol matrix is chemically cross-linked with sodium tetraborate and micro-sized particles of carbonyl iron are dispersed randomly in the sample. Ferrogels exhibit active behavior characterized by a deformation, a stiffness increase, and a change of other properties when subjected to a magnetic field making them promising future actuator materials. Furthermore, since the composition of ferrogels can be easily varied the active properties of these materials can be designed over a wide range of possibilities. In order for this to be possible however, a thorough understanding of the active behavior of these materials and its dependence on external factors is necessary. This paper focuses on the magnetic properties of PVA/carbonyl iron ferrogels and how they are dependent on internal and external factors. Magnetization of the ferrogel sample will be measured under a uniform, sinusoidal magnetic field for constrained and unconstrained samples with various iron concentrations and under a range of excitation frequencies. Uniform excitation fields of up to 500 G are created by passing current through a coil that is substantially larger than the sample size. Excitation frequencies of 0.1 Hz to 20 Hz and iron concentrations of 12 wt%, 20 wt% and 27 wt% are investigated. The magnetization is determined by measuring the voltage induced in a pickup coil that surrounds the ferrogel sample. The objective of these tests is to investigate the magnetic properties of a poly-vinylalcohol/carbonyl iron ferrogel to help in the future design of ferrogels for specific applications.