Local modification of magnetic anisotropy and ion milling of Co/Pt multilayers using a He+ ion beam microscope

We use a focused helium ion beam microscope to controllably remove material from Pt-capped thin film multilayers with perpendicular magnetic anisotropy. The dose range required to remove several nm of the cap layer is the same as that required to induce a spin reorientation transition. Milling depth for Pt is found to scale with the logarithm of ion dose, with very high removal yields of hundreds of atoms per He ion at low doses. While the deposited energy is of order of previous broadbeam helium irradiations, the current density impacting on the surface of the sample is several tens of A/cm2, orders of magnitude higher. Patterning of the platinum capping layer with 20 nm resolution is demonstrated.