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 stored magnetic state to another depends on the multilayer structure of the device and the intrinsic properties of the materials used, which are difficult to control on a local scale. Here we demonstrate how focused helium ion beam irradiation can be used to modulate the local magnetic anisotropy of a Co thin film at the microscopic scale. In-situ characterisation using the anomalous Hall effect showed up to an order of magnitude reduction of the magnetic anisotropy under irradiation in real-time, and using this, a multi-level storage element is demonstrated. The result is that current-driven spin-switching, with as little as 800 kA cm -2 can be achieved on predetermined areas of the film without the need for lithography. MAIN TEXTSpin transport across material interfaces is sensitive to the electronic and structural nature of the interface. Since the discovery of giant magnetoresistance in the late 1980's 1,2 through to the theoretical 3 and experimental realisation of spin transfer torque 4,5 , spintronics is a younger field that has grown steadily, with modern data storage already exploiting conventional spin transfer torque to change magnetisation states in magnetic tunnel junctions 6 . Spin orbit torque (SOT) switching, on the other hand, is a relatively young field [7][8][9] , relying on the spin Hall 9 and Rashba 10 effects to manipulate static and dynamic magnetisation states by the flow of electrical current in adjacent heavy metal (HM) layers. In contrast to spin-transfer-torque MRAMs 11 , SOT devices require less demanding 3D fabrication, greatly simplifying their production. Moreover, their planar

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He+ ion irradiation is used to pattern multiple areas of Pt/Co/W films with different irradiation doses in Hall bars. The resulting perpendicular magnetic anisotropy landscape enables selective multilevel current-induced switching with full deterministic control of the position and order of the individual switching elements. Key pattern design parameters are specified, opening a way to scalable multi-level switching devices.