Positive magnetic patterning using ion beams – principles and device applications

Magnetic data-storage, spintronic and magnonic devices have driven the need for producing well-defined nanoscale magnets of complex geometries. We show how ion-beams can be used to generate nanomagnets in thin films of certain alloys such as B2 ordered Fe60Al40 and Fe50Rh50.[1,2] In these materials a large increase of the saturation magnetization is achieved by inducing subtle atomic displacements caused by collision cascades of penetrating light ions. The ions knock atoms from their ordered sites, generating antisite defects and causing an increase of the Fe-Fe nearest-neighbour interactions which are linked to the increasing magnetization. For instance, a weak magnetization of 0.04 μB per Fe-atom in B2-Fe60Al40 can be increased to 1.67 μB per Fe-atom by the irradiation of light noble gas ions such as He+ or Ne+.
The above ion-induced increase of magnetization can be manifested at the local scale and is termed positive magnetic patterning. Patterning can be performed either by irradiation through lithographed masks,[1] or by a direct writing process using the highly focused ion-beam of a Gas Field Ion-Source.[3] Lateral magneto-resistive devices and magnetic arrays produced by ion-irradiation will be described. The application of ion-assisted magnetic writing opens vast opportunities not only in the field of nanomagnetism and devices, but also in the study of disorder-induced magnetic phase transitions at the nanoscale.
[1] R. Bali et al., Nano Letters (2014) 14 435.
[2] A. Heidarian et al., Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms (2015) 358 251.
[3] F. Röder et al., Scientific Reports (2015) 5 16786.