Influence of magnetic anisotropy and its distribution on the hysteresis loops upon patterning thin films

We compare the hysteresis loops of ferromagnetic films and dots down to 0.2 μm. Samples are made of Co–Pt multilayers with different Co thicknesses so as to vary the perpendicular magnetic anisotropy. We determined the first- and second-order anisotropies of the films, as well as the first-order anisotropy distribution, and show that from these quantities the switching field distribution of dots can be predicted. We also explain through a simple criterion—the relation between the anisotropy distribution and the minimum nucleation field—why in some cases the hysteresis loops recorded along the easy axis on the films undergo a dramatic change after patterning.