Magnetic lithography on paramagnetic FeAl alloys by selective ion irradiation

The atomically-ordered Fe60Al40 (at. %) alloy is paramagnetic at room temperature but it becomes ferromagnetic when subject to structural disorder [1]. This effect has been recently used to generate arrays of sub-100 nm ferromagnetic dots embedded in a paramagnetic matrix. To selectively induce structural disorder, local irradiation procedures, either through lithographed masks or using focused ion beam, have been utilized. Due to the low ion doses used, the irradiation processes do not induce any surface corrugation, thus circumventing tribological problems. The fabricated entities exhibit a range of magnetic properties depending on the size and shape. Furthermore, when the patterned sheets are annealed at sufficiently high temperatures (i.e., around 900 K), the magnetic properties are erased due to the annealing-induced atomic reordering. This method may be extrapolated to a variety of other intermetallic systems such as Fe2AlMn, Ni3Sn2 or CoGa and also to austenitic steels. The obtained magnetic structures may have technological applications, such as magnetic sensors or patterned recording media.
Partial financial support from the Spanish 2005SGR-00401, MAT2007-66302-C02 and MAT2007-61629 research projects, the EU-RITA program “Center for the Application of Ion Beams in Materials Research” (under contract no. 025646) and the Swedish Agencies VINNOVA and SSF is acknowledged. E. M. acknowledges his FPI fellowship from the Spanish Ministerio de Educación y Ciencia, co-financed by the ESF.
[1] J. Nogués et al., Phys Rev. B Phys. Rev. B 74, 024407 (2006)