We have developed an irradiation technique that allows us to fabricate sets of submicron, planar magnetic nanostructures exhibiting perpendicular magnetization and very reproducible coercivity. The method is based on local 10-keV He ion irradiation of CoPt{sub}3 alloys with initial perpendicular magnetization. Irradiation reduces the magneto-crystalline anisotropy in the matrix area around the dots. Irradiation fluence is chosen such that narrow stripes appear, creating demagnetized areas, that surround the dots. The magnetization reversal process of these dots exhibit special features since no nucleation event is ever required. Domain walls are injected from the interdot space, which acts as a domain wall reservoir. The dot coercivity in thus a propagation field, ensuring a weak spread of coercivity.
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