Precise control of domain wall injection and pinning using helium and gallium focused ion beams

In experiments on current-driven domain wall (DW) motion in nanostrips with perpendicular magnetic anisotropy (PMA), the initial DW preparation is usually not well controlled. We demonstrate precise control of DW injection using Ga and novel He focused ion beam (FIB) irradiation to locally reduce the anisotropy in part of a Pt/Co/Pt strip. DWs experience pinning at the boundary of the irradiated area. This DW pinning is more pronounced at the He irradiation boundary compared to Ga. This is attributed to a better He beam resolution, causing an anisotropy gradient over a much smaller length scale and hence, a steeper energy barrier for the DW. The results indicate that He FIB is a useful tool for anisotropy engineering of magnetic devices in the nanometer range. (C) 2011 American Institute of Physics. [doi:10.1063/1.3549589]