Metamaterials

Fig 1: SEM images of permalloy nanostructures on silicon written by electron beam lithography

Metamaterials are artificial crystals geometrically structured on the sub-micrometer scale with the purpose of tuning emerging optical properties.

Our research is focussed on lithographically synthesized permalloy (Fe19Ni81) nanoislands on a silicon substrate. These islands are arranged in a two-dimensional periodic pattern to form meta unit cells (see figure 1). In the ideal case, each nanoisland is a single domain magnet with a magnetic moment oriented along its easy axis. The longe-range ordered ground state of this system is determined by the magnetic dipole interaction between structural units. Our goal is to design metamaterials with magnetic flux vortices of accessable chirality and hence with an integral toroidal moment. The realization of this ordering would lead to an intrinsic violation of space and time inversion symmetry and - related to this - to interesting optical responses.
In the lithography process, one can define geometries, sizes and lattice-types. By using a magnetic nanoprobe and/or global electromagnetic fields one can fine-tune the magnetic order. We can image and verify this order by magnetic force microscopy (see figure 2).

Fig 2: MFM image of a toroid-like magnetic structure based on a pattern such as in figure 1a. The superimposed colorcode indicates the correspondend magnetic chirality.