This work introduces a computational micromagnetic model of Focused Ion Beam (FIB) irradiated Co/Pt multilayers and shows how FIB irradiation can be used to engineer field-coupled devices made from Co/Pt multilayers. Irradiation locally changes the magnetic properties of Co/Pt layer stacks and can be used as a one-step tool for defining magnetic nanostructures. High irradiation dose renders the material non-magnetic or paramagnetic, while a lower dose locally reduces anisotropy, exchange and saturation magnetization. We implemented the model of inhomogenously irradiated Co/Pt nanomagnets in a standard micromagnetic simulation software, OOMMF . Using our simulation tool we show how FIB irradiation enables the definition of nucleation sites on a nanomagnet. This changes the reversal mode of the magnet – FIB-defined dots start switching from the side that received the highest dose . Additionally, irradiation changes the strength of the magnetic dipole coupling between neighboring nanomagnets. For example, a nanomagnet partially irradiated at its left side shows a stronger coupling to its left neighbor than to the right one. We show how partial irradiation can be exploited in the design of field-coupled magnetic computing devices. In magnetic field coupling, information is represented by the magnetic orientation of single-domain nanomagnets and the magnetic signal is propagated and processed by their field-interactions . Operation of the device requires precise control over the magnetic ordering. This is difficult to achieve , since field-interactions are reciprocal – the magnets jointly interact with all their neighbors so the direction of signal flow is not defined. Asymmetric irradiation of a nanomagnets can lead to non-reciprocal signal propagation and perfectly controlled, frustration-free ordering. Even large field-coupled structures can be demagnetized (put in their computational ground state) with a homogenous external field. We will show how shift registers and logic gates can be constructed from asymmetrically irradiated dots.  http://math.nist.gov/oommf/;  M. Becherer, J. Kiermaier, G. Csaba, J. Rezgani, C. Yilmaz, P. Osswald, P. Lugli, D. Schmitt-Landsiedel: Characterizing magnetic field-coupled computing devices by the Extraordinary Hall-effect presented at ESSDERC, Athens Sept 14-18 2000;  A. Imre, G. Csaba, L. Ji, A. Orlov, G. H. Bernstein, and W. Porod : Majority Logic Gate for Magnetic Quantum-Dot Cellular Automata Science 311 (5758), 205 (2006);  M. Becherer, G. Csaba, W. Porod, R. Emling, P. Lugli, D. Schmitt-Landsiedel,: Magnetic Ordering of Focused-Ion-Beam Structured Cobalt-Platinum Dots for Field-Coupled Computing IEEE Transactions on Nanotechnology, vol.7, no.3, pp.316-320, May 2008.