Colloidal domain lithography for regularly arranged artificial magnetic out-of-plane monodomains in Au/Co/Au layers

Abstract

Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, the fabrication of regularly arranged artificial domains in topographically flat films is difficult, since the free energy minimization determines the existence, shape, and regularity of domains. Here we show that keV He(+) ion bombardment of Au/Co/Au layer systems through a colloidal mask of hexagonally arranged spherical polystyrene beads enables magnetic patterning of regularly arranged cylindrical magnetic monodomains with out-of-plane magnetization embedded in a ferromagnetic matrix with easy-plane anisotropy. This colloidal domain lithography creates artificial domains via periodic lateral anisotropy variations induced by periodic defect density modulations. Magnetization reversal of the layer system observed by magnetic force microscopy shows individual disc switching indicating monodomain states.

Magnetization states and magnetization processes in nanostructures: From a single layer to multilayers

“…Ga + ‐fluence‐induced increase of Kerr rotation was also observed . We have demonstrated that controlled changes of the magnetic anisotropy realized by ion bombardment with different fluences may be applied for production of magnetic films with parameters attractive for hard disc technology or transport of magnetic (commercially available) markers (beads) .…”

Tailoring magnetic anisotropy gradients by ion bombardment for domain wall positioning in magnetic multilayers with perpendicular anisotropy

“…In Figure 2b, the measured H C is plotted as a function of the x -position for both stripes. A monotonic decrease of coercive field with F is observed, which is caused by the reduction of the interface anisotropy due to modification of Co/Au and Au/Co interfaces through the increasing fluence of the 10-keV He + ions [19,25,26]. Comparing the H C ( F ) and H C ( x ) dependencies for the two stripes with different gradients (Figure 2b,c), it can be seen that the H C ( F ) basically does not depend on d F /d x .…”

“…The base pressure during sputtering was < 1 × 10 −6  Pa with Ar process gas (Ar partial pressure approximately 10 −2  Pa). The Co thickness t Co was chosen to be well above the critical thickness where the Co layer becomes superpara- or paramagnetic after light-ion bombardment [19] and at the same time thin enough to preserve a large PMA. Moreover, t Co selected here ensures that the magnetization reversal in the unbombarded Au/Co/Au system in a perpendicular magnetic field develops primarily by DW movement [2].…”

“…After the six tracks, the cumulated maximum fluence F max for stripe 1 was 1.06 × 10 15 He + /cm 2 and for the second stripe 5.03 × 10 14 He + /cm 2 . The stage velocity was chosen for an average fluence gradient of d F /d x  = 8.8 × 10 13 (He + /cm 2 )/mm for stripe 1 and 4.4 × 10 13 (He + /cm 2 )/mm for stripe 2 and maximum fluences based on previous investigations [19,21]. Due to the flux decrease of the ion beam at the edges of the rectangle, also a fluence gradient along the y -direction is observed.…”

Preferential weakening of rotational magnetic anisotropy by keV-He ion bombardment in polycrystalline exchange bias layer systems

“…In magnetoresistive sensor stacks (sensors based on the giant magnetoresistance effect or magnetic tunnel junctions) with magnetic reference electrodes pinned by exchange bias, for example, the pinning direction can be set to an arbitrary direction after completion of the deposition process essentially without changing the magnetoresistive effect amplitude [11][12][13]. Its possible use in creating magnetic logic elements has similarly been proven [14] as its potential to create engineered domain patterns by ion beam writing or when combined with lithographical techniques [1,4,[15][16][17]. The latter patterns have shown to be useful for magnetic particle transport by moving domain walls [18], by changing potential energy landscapes associated with the stray fields above the engineered domains [19,20] or by topological transport [21].…”