By ion irradiation through a lithographically made resist mask, the magnetic properties of cobalt-platinum simple sandwiches and multilayers were patterned without affecting their roughness and optical properties. This was demonstrated on arrays of 1-micrometer lines by near- and far-field magnetooptical microscopy. The coercive force and magnetic anisotropy of the irradiated regions can be accurately controlled by the irradiation fluence. If combined with high-resolution lithography, this technique holds promise for ultrahigh-density magnetic recording applications.