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The magnetoelastic behavior of bimodal magnetic elastomers consisting of magnetic particles, carbonyl iron, and nonmagnetic particles, zinc oxide, has been investigated by dynamic viscoelastic measurements. The storage modulus of bimodal magnetic elastomers increased under a magnetic field of 500 mT. The change in the storage modulus was enhanced by adding nonmagnetic particles at volume fractions above a certain volume fraction of 0.02, indicating the occurrence of stress transfer by a chain structure of magnetic particles via nonmagnetic particles. The critical volume fraction at 500 mT determined by percolation analysis was nearly independent of the diameter of nonmagnetic particles. However, at low magnetic fields below 160 mT, the critical volume fraction was found to decrease with the particle diameter. Substituting magnetic particles with nonmagnetic ones, the change in the storage modulus of bimodal magnetic elastomers monotonically decreased with the substitution ratio of magnetic particles. The mechanism of the enhanced magnetoelastic response for bimodal magnetic elastomers is discussed.

Magnetic elastomers containing magnetic particles with a diameter of 235 µm have been synthesized, and the magnetic response of the elasticity was investigated. The storage modulus for the magnetic elastomer with a volume fraction of 0.18 increased from 12.5 kPa to 2.43 MPa by applying a magnetic field of 500 mT. The relative change in the storage modulus was 194 times, which is higher than that of magnetic elastomers containing small iron particles (ca. 58 times at 2.5 µm). It was also revealed that the magnetic elastomer exhibited wide-range modulation of loss tangent by varying magnetic fields.