Nonreciprocal electromagnetic properties of nanocomposites at microwave frequencies

Abstract

We report on the effects of composition and external magnetic field on the microwave permeability tensor of $\mathrm{Ni}∕\gamma {\text{−}\mathrm{Fe}}_2{\mathrm{O}}_3$ nanocomposites. When compared to the zero-field case, the field measurements of the permeability tensor $\overline{\mu }$ exhibit nonzero off-diagonal components giving evidence of the nonreciprocity of wave propagation in these nanostructures. We observe that the diagonal and off-diagonal elements of $\stackrel{⃡}{\mu }$ of these nanocomposites depend sensitively on their Ni content and of the applied static magnetic field. These experimental results are analyzed within a recently developed multiscale modeling [S. Mallegol et al., Phys. Rev. B 68, 174422 (2003)] and can be understood as arising from magnetostatic intergranular interactions via a mean-field approximation. The application of these heterogeneous nanomaterials open possibilities for the design of field-controlled nonreciprocal components used in microwave integrated circuit technology.