Magnetic interactions in 2D and 3D arrays

Abstract

Magnetostatic interactions manifest themselves via the fields and forces between and within magnetized bodies. This thesis topics magnetostatic interactions in arrays at the nano- and millimeter scale. These arrays may find application in magnetic data storage and in future 3D electronics fabricated by self-assembly. On the nanoscale, interactions are investigated that are involved in reading and writing 2D patterned arrays of magnetic ~100 nm Co/Pt multilayered islands with perpendicular anisotropy, by magnetic force microscopy (MFM), and by modeling and simulations. Such 2D arrays are prototypes for future hard disk drive media, i.e. bit patterned media. Concerning reading, a new model for media noise is presented. The model captures the fluctuation in the shapes of the islands by the power spectrum of their perimeter, and predicts correlated amplitude and position jitter in the read back pulses of the islands. Besides media noise, 2D inter symbol interference (ISI) inhibits the correct detection of bits. A simple 2D modulation code that avoids the worst case interference patterns at the cost of a 5/6 code rate can handles more jitter compared to a previously developed code. Using MFM, first an off-line correction for the topographic distortion due to the liftmode MFM operation is investigated. Next, in-field MFM is used to determine the remanent switching fields of individual islands in an array. Remarkably, the measurements reveal that the switching mechanism varies within the array. Lastly, the read back signal and write field of side-coated MFM tips are investigated by imaging patterned arrays and varying the coating thickness. Due to undesired tip-sample interactions, the coating thickness is limited to about 80 nm, which limits the field of the tip to about 200 kA/m, typically smaller than the switching field distribution of a bit patterned array. On the millimeter scale, interactions are investigated that bind and drive the self-assembly of 2D and 3D arrays. Simulations show that 3–4 spherical particles equipped with magnets prefer to assemble in 2D configurations. By indenting the particles, a 3D configuration is possible if the magnets can rotate freely. In addition, magnetic levitation is used to drive the self-assembly of 0.5 mm Si cubes into, desirably, 2D and 3D arrays. Higher quality arrays are obtained when the hydrophilicity of the particles is reduced or when the bottom of the liquid container is used as a template. In calculations, it is confirmed that the particles indeed minimize the magnetostatic energy in a self-assembly experiment.