Lithographically structured films
During the last decade artificially fabricated periodic magnetic nanostructures have attracted the attention of a growing scientific community. More recently, the attention has been focused on patterned magnetic films. These nanomagnets with all three dimensions in the micron and/or nanometer range are interesting for mainly two reasons: on the one hand these are perfect systems to test theorems in magnetostatics and micromagnetics, while, on the other hand, technological applications such as magnetic data storage media or magnetic sensors are in progress. Moreover, as the dimensions become comparable to some characteristic length scale of the material (e.g. the typical domain size or the magnetic domain wall width), these structures may exhibit novel properties.
Results on Co dots
We prepared a sample with circular dots (by UV lithography) with a diameter of 4mm and a sample with rectangular dots (by electron beam lithography) with a length of 4 mm and a width of 1 mm. Both kinds of dots were placed in a square lattice with a period of 10 mm with a total patterned area of 4 cm2. Each dot consisted of a trilayer of the form 7.5 nm Au / 20 nm Co / 7.5 nm Au.
Optical microscope picture of the sample, showing the arrangement of the Co disks in a square lattice with a 10 µm period. The inset (upper left corner) shows an atomic force microscope (AFM) image of a single disk. In the lower right corner the in-plane directions are defined.
We investigated these samples by off-specular PNR to investigate the magnetization reversal. By using a position sensitive detector we were able to record not only the specularly but also the off-specularly scattered intensity which has maxima at particular angles due to the in-plane periodicity of the disks. PNR has the property to distinguish between different magnetization reversal models because the neutrons are sensitive to the parallel as well as perpendicular magnetization component with respect to an external magnetic field. The perpendicular compo-nent causes a spin-flip intensity (I+- and I-+), whereas the parallel component causes a difference between the non-spin flip inten-sities I++ and I--.