Micromagnetic Modeling of Write Heads for High-Density and High-Data-Rate Perpendicular Recording
Creators: name: Bai, Daniel Zhigang
Publisher: name: Carnegie Mellon University
Year: 2004
Subjects: subject: Computer Engineering
subject: 90699 Electrical and Electronic Engineering not elsewhere classified
subject: FOS: Electrical engineering, electronic engineering, information engineering
subject: FOS: Electrical engineering, electronic engineering, information engineering

description: In this dissertation, three dimensional dynamic micromagnetic modeling based on Landau-Lifshitz equation with Gilbert damping has been used to study the magnetic processes of the thin film write heads for high density and high data rate perpendicular magnetic recording. In extremely narrow track width regime, for example, around or below 100 nm, the head field is found to suffer from significant loss from the ideal AttM s value for perpendicular recording. In the meantime, remanent head field becomes significant, posing potential issue of head remanence erasure. Using micromagnetic modeling, various novel head designs have been investigated. For an overall head dimension around one micron, the shape and structure of the head yoke have been found to greatly affect the head magnetization reversal performance, therefore the field rise time, especially for moderate driving currents. A lamination of the head across its thickness, both in the yoke and in the pole tip, yields excellent field reversal speed, and more importantly, it suppresses the remanent field very well and thus making itself a simple and effective approach to robust near-zero remanence. A single pole head design with a stitched pole tip and a recessed side yoke can produce significantly enhanced head field compared to a traditional single pole head. Various head design parameters have been examined via micromagnetic modeling. Using the dynamic micromagnetic model, the magnetization reversal processes at data rates beyond 1 G bit/s have been studied. The excitation of spin wave during the head field reversal and the energy dissipation afterwards were found im portant in dictating the field rise time. Both the drive current rise time and the Gilbert damping constant affect the field reversal speed. The effect of the soft underlayer (SUL) in both the write and the read processes have been studied via micromagnetic modeling. Although it is relatively easy to fulfill the requirement for the magnetic imaging in writing, the SUL deteriorates the readback performance and lowers the achievable recording linear density. Various parameters have been investigated and solutions have been proposed. The effect of stress in magnetostrictive thin films has been studied both analytically and by simulation. The micromagnetic model has been extended to incorporate the stress-induced anisotropy effect. Simulation was done on both a magnetic thin film undergoing stresses to show the static domains and a conceptual write head design that utilizes the stress induced anisotropy to achieve better performance. A self-consistent model based on energy minimization has been developed to model both the magnetization and the stress-strain states of a magnetic thin film.