Micro-/nano-scale magnetic patterning of paramagnetic FeAl intermetallic alloys

Atomically ordered Fe60Al40 (at. %) alloys are paramagnetic at room temperature, while disordered Fe60Al40 becomes ferromagnetic. This effect can be 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 900 K), the magnetic properties are lost due to the annealing-induced atomic reordering. Hence, these methods may lead to a novel type of patterned recording media free from exchange coupling effects. Moreover, they can be easily extrapolated to a variety of other systems, such as CoZr, CoAl, CoGa, CoV, NiSn, FeGe, FePt3, FeV or even austenitic stainless steel.

[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).