Switching properties of patterned longitudinal magnetic media.

摘要

Areal recording densities in hard-disk systems have been increasing at dramatic rates in the past few years. Two factors which currently limit the density of recording systems are—the transition noise, and the superparamagnetic limit. To address these problems, patterned magnetic media, composed of closely packed regular array of single domain particles, has been proposed as an alternative. The primary purpose of this thesis is to understand the behavior of patterned longitudinal magnetic island arrays from a data storage perspective. For this purpose we have used a lithographically fabricated regular array of cobalt (101&barbelow;0) islands as a prototype patterned media system.; Nanometer scale magnetic islands have been fabricated from epitaxial cobalt and Co₉₀Cr₁₀ (101&barbelow;0) films by lithographic processes. Observation of the domain patterns and switching mechanisms in these islands was done using a magnetic force microscope (MFM). Interesting observations like the bi-domain switching and direct switching have been explained using micromagnetic modeling. The switching field distribution (SFD) of the island array has been measured using an in-situ field MFM. A dragtester fitted with a giant magneto-resistance (GMR) read/write head has been used to write and read a square wave pattern on close packed arrays of cobalt islands. The readback signal is used to calculate the signal-to-noise ratio and jitter. These values have been compared with those of conventional longitudinal media on which a square wave pattern has been written and readback by the same dragtester setup. The SNR and jitter values for patterned media are better than those of the conventional media.; Write synchronization requirement, i.e. the maximum allowable head offset (in the down-track direction) with respect to the island position that can be tolerated while writing on these islands has also been estimated. For this purpose we have compared longitudinal patterned cobalt (101&barbelow;0) media and perpendicular Co₇₀Cr₁₈Pt₁₂ patterned media. The results were simulated using a model that included the SFD of the media and the head field gradient. The results have shown that a sharper head field gradient and a narrower SFD improve the write window.