Colossal Magnetoelastic Effects in Magnetoactive Elastomers

Composite materials where soft-magnetic micrometer-sized particles are embedded into a compliant polymer matrix are known as magnetoactive or magnetorheological elastomers. They are distinguished by huge variations of their physical properties in a magnetic field, which is commonly attributed to the restructuring of the filler. The process of the magnetic-field-induced restructuring in a magnetorheological elastomer is interpreted as a progression towards percolation. The theoretical approach is built upon a self-consistent effective-medium theory for the elastic properties, extended to the variable (field dependent) percolation threshold. The proposed model allows one to describe the large variations (over several orders of magnitude) of the effective elastic moduli of these composite materials, known as the giant magnetorheological and field-stiffening effects. An existence of a giant magnetic Poisson effect is predicted.