Inductive and magnetorheological properties of soft and hard magnetic fillers in elastomers

Magnetorheological elastomers are smart materials, that have great potential for many technical applications like intelligent semi-active dampers or energy harvesting applications. We investigate soft- and hard-magnetic filler types in typical technical elastomers under cyclic deformation regarding their influence on the electromagnetic induction and magnetic switching-ability of the compounds. The effect of vulcanization in an external magnetic field is considered leading to anisotropic samples with aligned filler particles. It is found that the soft magnetic fillers show a higher switching-ability compared to hard magnetic fillers in anisotropic samples, which is related to hysteretic and slow magnetization behaviour of hard magnetic fillers. This also leads to a negative switching effect or softening of the samples if the direction of the magnetic field is opposite to that during vulcanization, suggesting rotational motion of the particles in dependence of the outer field. The stress values and mechanical hysteresis are generally higher for the anisotropic samples, both for soft and hard magnetic fillers. This is found for quasistatic and dynamic excitations at different frequencies and can clearly be related to the alignment of particles. Nevertheless, the energy harvesting ability seems to be widely independent of this since no significant different inductive properties are found for isotropic and anisotropic samples. The possibility of a combined magnetorheological and energy harvesting application is discussed.