  We propose a theoretical approach for calculating effective electric and
magnetic properties of composites with field-dependent restructuring of the
filler. The theory combines the Bruggeman-Landauer approximation extended to a
field-dependent (variable) percolation threshold with the approximate treatment
of nonlinearity of material properties. Theoretical results are compared with
experiments on magnetorheological elastomers, which in the context of
investigated phenomena are often called magnetoactive elastomers (MAEs). In
MAEs with soft polymer matrices, the mutual arrangement of inclusions changes
in an applied magnetic field. This reorganization of the microstructure leads
to unconventionally large changes of electrical and magnetic properties.
Obtained theoretical results describe observed phenomena in MAEs well.
Qualitative agreement between theory and experiment is demonstrated for the
magnetodielectric effect. In the case of magnetic permeability, quantitative
agreement is achieved. The theoretical approach presented can be useful for
development of field-controlled smart materials and design of smart structures
on their basis, because the field dependence of physical properties can be
predicted.
