Self-organized spatio-temporal micropatterning in ferromagnetic Co-In films

Cobalt-indium (Co-In) heterogeneous films, featuring spatio-temporal patterns, have been electrodeposited in a chloride-citrate electrolyte. The Co content can be tuned from 25 at% to 90 at% by varying the applied current density between -10 and -30 mA cm^-2. The spatio-temporal patterns consist of alternated dark and bright belts, which define micron-sized waves, targets and spirals. Cross-sectional images indicate layer-by-layer growth. Several crystallographic phases (hexagonal close-packed Co, face-centered cubic Co, tetragonal In and tetragonal CoIn₃) are identified in the corresponding X-ray diffractograms. The films exhibit a combination of large hardness with relatively large Young's modulus and a soft-magnetic behaviour with tunable saturation magnetisation and coercivity (H_C) values, mostly depending on the Co content and the effective magnetic anisotropy. The film with 90 at% Co shows the highest in-plane H_C (275 Oe) and a squareness ratio close to 1. Magnetic force microscopy observations reveal that the self-patterning is not only topographic but also magnetic. These results demonstrate that the electrodeposition of spatio-temporal structures is a simple method to grow magnetically patterned films, over large areas, in a rapid and inexpensive way. This procedure is highly attractive for the implementation of new types of magnetic sensors, encoding magnetic stripes or even magnetic recording media.