  Spin orbit torque driven switching is a favourable way to manipulate
nanoscale magnetic objects for both memory and wireless communication devices.
The critical current required to switch from one magnetic state to another
depends on the geometry and the intrinsic properties of the materials used,
which are difficult to control locally. Here we demonstrate how focused helium
ion beam irradiation can modulate the local magnetic anisotropy of a Co thin
film at the microscopic scale. Real-time in-situ characterisation using the
anomalous Hall effect showed up to an order of magnitude reduction of the
magnetic anisotropy under irradiation, and using this, multi-level switching is
demonstrated. The result is that spin-switching current densities, down to 800
kA cm$^{-2}$, can be achieved on predetermined areas of the film, without the
need for lithography. The ability to vary critical currents spatially has
implications not only for storage elements, but also neuromorphic and
probabilistic computing.
