Dot arrays made of polycrystalline CoPt multilayer with an average grain size of 20 nm are fabricated by using a laser interference lithography and their magnetic properties are examined by detecting anomalous Hall effect. It is revealed that the ratio of dots which have stable single domain state increases from 35% to 85% while the dot diameter decreased from 200 to 120 nm. The energy barrier height of magnetization reversal is estimated as 4.0× 10-12 erg from sweep rate dependence of the coercivity. The energy corresponds to the switching volume comparable with the volume of a physical grain in the multilayer film.
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