Magnetic properties of PDMS embedded with strontium ferrite particles cured under different magnetic field configurations

Flexible materials embedded with hard magnetic particles have recently gained widespread recognition as small-scale actuators due to their capacity to be a rapid and precise shape-shifting material. Strontium ferrite (SrFe12O19) particles have been shown as a great candidate for such applications, since it is an inert hard magnetic material that, in contrast to barium ferrite and neodymium, is also biocompatible. The preparation of such material is done by mixing the magnetic particles into the uncured elastomer (polydimethylsiloxane (PDMS)), in liquid form, and then pouring the mixture in a mold for curing. If the samples are subjected to a magnetic field during the curing process, chains of particles are formed in the direction of the applied field, thus creating an easy axis in this same direction. The magnetic properties of such composite cannot yet be found in literature. In this study, we analyzed three concentrations of strontium ferrite particles in PDMS under three field configurations, resulting in 9 different samples. The concentrations used were 1:1, 2:1, and 4:1 ratios of PDMS to strontium ferrite per weight. All three types of samples were cured either in a zero magnetic field, or over the north pole of a neodymium permanent magnet, or over the side of said magnet. A biaxial vibrating sample magnetometer (VSM) was used to measure hysteresis curves parallel and perpendicular to the curing field. The samples cured in a field show a squareness ratio of up to 0.94 while the samples cured in zero field, only close to 0.5. The samples cured in a field show a magnetic anisotropy with an easy axis parallel to the curing field. Harvesting these modified properties, a mobile robot manufacturing method is proposed that bypasses the need of applying a high intensity magnetic field.