Micro- and nanoscale magnetic patterning of paramagnetic FeAl alloys by means of nanoindentation or selective ion irradiation

Some intermetallic alloys exhibit a transition from paramagnetic to ferromagnetic states when they are atomically disordered. This is the case, for example, of the atomically-ordered Fe60Al40 (at. %) alloy, which is paramagnetic at room temperature but becomes ferromagnetic when subject to structural disordered. This effect has been used to generate arrays of ferromagnetic dots embedded in a paramagnetic matrix. This can be accomplished by two different routes: (i) selective mechanical deformation by means of nanoindentation and (ii) local irradiation procedures, either through lithographed masks or using focused ion beam. Concerning route (i), two types of geometries were designed: periodic arrays of triangular dots (resulting from the pyramidal shape of the Berkovich indenter) and arrays of straight lines produced by scratch [1]. Route (ii) has the advantage over nanoindentation that, due to the low doses used, it does not induce any roughening of the surface, avoiding tribological problems. The fabricated entities exhibit a range of magnetic properties depending on the size and shape, which were investigated by means of a magneto-optical Kerr effect setup, while the local character of the induced ferromagnetism was examined by magnetic force microscopy. Furthermore, when the patterned sheets are annealed at sufficiently high temperatures (i.e., around 800 K), the magnetic properties are lost due to the annealing-induced atomic reordering. This method may be easily extrapolated to a variety of other intermetallic systems such as Fe2AlMn, Ni3Sn2, CoAl or CoGa and the obtained magnetic structures may have interesting applications, such as patterned recording media (free tribological problems and detrimental exchange interactions) or magnetic sensors.

[1] J. Sort, A. Concustell, E. Menéndez, S. Suriñach, K.V. Rao, S.C. Deevi, M.D. Baró and J. Nogués. Periodic arrays of micrometer and sub-micrometer magnetic structures prepared by nanoindentation of a nonmagnetic intermetallic compound. Adv. Mater. 18, 1717-1720 (2006).