Direct Magnetic Patterning due to the Generation of Ferromagnetism by Selective Ion Irradiation of Paramagnetic FeAl Alloys

Sub‐100‐nm magnetic dots embedded in a non‐magnetic matrix are controllably generated by selective ion irradiation of paramagnetic Fe₆₀Al₄₀ (atomic %) alloys, taking advantage of the disorder‐induced magnetism in this material. The process is demonstrated by sequential focused ion beam irradiation and by in‐parallel broad‐beam ion irradiation through lithographed masks. Due to the low fluences used, this method results in practically no alteration of the surface roughness. The dots exhibit a range of magnetic properties depending on the size and shape of the structures, with the smallest dots (<100 nm) having square hysteresis loops with coercivities in excess of µ₀H_C = 50 mT. Importantly, the patterning can be fully removed by annealing. The combination of properties induced by the direct magnetic patterning is appealing for a wide range of applications, such as patterned media, magnetic separators, or sensors.