Creation of sub-100 nm ferromagnetic dots by selective irradiation of a paramagnetic intermetallic alloy

Sub-50 nm ferromagnetic dots embedded in a non-magnetic matrix have been controllably generated by selective, low fluence, ion irradiation of paramagnetic Fe60Al40 (atomic %) intermetallic sheets. The process is demonstrated by sequential focused ion beam irradiation and by broad beam irradiation through lithographically defined masks. Due to the low fluences required, this method does not induce any corrugation of the surface. The dots exhibit a range of magnetic properties depending on the size and shape of the structures, with the smallest ones (<50 nm) having square hysteresis loops with coercivities in excess of µ0HC = 50 mT. This presents a promising novel type of patterned recording media free from tribological and exchange coupling effects.