Magnetization reversal in ultrathin Co/Cu(0 0 1)-microstructures

Abstract

The magnetic domain structure of ultrathin Co-microstructures on Cu(0 0 1) has been investigated by means of a scanning electron microscope with polarization analysis. In particular, the influence of a magnetic field on the domain structure has been studied. Here, we concentrate on squares of different size (3– 30 μm ) and variable thickness, although triangles and bars with aspect ratios up to 1:30 have been studied, too. In the as-grown state the microstructures with an edge length larger than 3 μm exhibit a multidomain structure, while the smaller ones are always single domain. After saturating the structures by a strong field, the magnetization can be switched homogeneously by either ±90° or 180° independent of size and shape. The microstructures remain in a single-domain state. Roughly 20% of the ultrathin particles show a two-step 180°-switching via a 90°-state. An analytical model is developed yielding coercivities of the right order of magnitude. The two-step reversal process can be explained in the framework of this model.