Fabrication of magnetic nanostructures using the focused ion beam technique

A potential approach to extend the current areal density of magnetic recording beyond 300 Gb/in² is physical patterning of the media. Among all the techniques that have been employed to pattern the continuous media into nanometer scale discrete tracks and bits, the focused ion beam (FIB) nanofabrication is one of the most straightforward techniques that does not require the use of various types of masks and molds. There has been much interest in nano-patterning of hard and soft magnetic materials and perpendicular recording media using the FIB, but very few of them has been focused on the milling processes. In this work, the FIB patterning of commercial post-sputtering longitudinal media is demonstrated. Special efforts have been put on optimizing the milling process through controlling the magnification, milling depth, and the ion beam scan mode. It was found that the parallel milling mode was effective in reducing the re-deposition at small depth and thus led to smaller nano-structures. The FIB processed nanostructures have been characterized using AFM and MFM. Patterns with square islands of 50nm and spacing of 10nm have been obtained. It is interesting to note that, in both serial and parallel milling modes at large depth, the re-deposition has accumulated at the junctions of the original dots and formed new dots. As dots formed by re-deposition have already lost their magnetic properties, they should be suppressed as much as possible. In the contrast to this, the re-deposition was almost eliminated in the parallel-milling mode at small depth. It can be seen clearly from the MFM observation that the in-plane magnetization has been pertained for the patterned structures at dimensions as small as 50nm and single domain structures were observed. The structures obtained in this work can be used to study magnetic recording at contact mode and at very high recording density.