Designing nanostructured magnetic materials by symmetry

We have investigated experimentally the influence of the geometric shape of deep sub-micron nanomagnets on their magnetic properties. We have used high-resolution electron beam lithography to make arrays of nanomagnets in the size range 40-500 nm which had rectangular, triangular, square and pentagonal geometries, corresponding, respectively, to rotational symmetries of order 2, 3, 4 and 5. The parent material was Supermalloy (Ni 80 Fe 14 Mo 5 ). We find that an enormously wide range of magnetic properties, including some not found in conventional unstructured materials, can be obtained by using different geometries. We demonstrate that this is because the geometric shape imposes a strong anisotropy field of related symmetry order on the nanomagnet via a recently discovered phenomenon called configurational anisotropy. We show that the coercive field and remanence of these structures is determined directly by this anisotropy.