The ion projector at the Fraunhofer Institute ISiT has been used for the development of patterned magnetic media for potential future use in magnetic hard disk drives. By 8.8 times demagnification of an open stencil mask, magnetic contrast is generated by ion intermixing of Co/Pt sandwich layers. In this application a resist process is not necessary and the surface roughness of magnetic media is not altered. Monte Carlo simulations of the intermixing process with the dynamic T-Dyn software for H, He, Ne, Ar and Au ions show that the exposure dose can be reduced by a factor of 100 by irradiation with Ar+ ions instead of He+. This has been confirmed by magnetic force microscopy of 200 nm magnetic dots irradiated at a dose of 6×1013 Ar+/cm2 at 73 keV energy. Sufficient stability of the ion optical system concerning resolution and drift has been demonstrated by exposures in developed and undeveloped (latent image) resist down to 60 nm dots.