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Title: Modelling data storage in nano-island magnetic materials
Author: Kalezhi, Josephat
ISNI:       0000 0004 2707 3306
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2011
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Data storage in current hard disk drives is limited by three factors. These are thermal stability of recorded data, the ability to store data, and the ability to read back the stored data. An attempt to alleviate one factor can affect others. This ultimately limits magnetic recording densities that can be achieved using traditional forms of data storage. In order to advance magnetic recording and postpone these inhibiting factors, new approaches are required. One approach is recording on Bit Patterned Media (BPM) where the medium is patterned into nanometer-sized magnetic islands where each stores a binary digit.This thesis presents a statistical model of write errors in BPM composed of single domain islands. The model includes thermal activation in a calculation of write errors without resorting to time consuming micromagnetic simulations of huge populations of islands. The model incorporates distributions of position, magnetic and geometric properties of islands. In order to study the impact of island geometry variations on the recording performance of BPM systems, the magnetometric demagnetising factors for a truncated elliptic cone, a generalised geometry that reasonably describe most proposed island shapes, were derived analytically.The inclusion of thermal activation was enabled by an analytic derivation of the energy barrier for a single domain island. The energy barrier is used in a calculation of transition rates that enable the calculation of error rates. The model has been used to study write-error performance of BPM systems having distributions of position, geometric and magnetic property variations. Results showed that island intrinsic anisotropy and position variations have a larger impact on write-error performance than geometric variations.The model was also used to study thermally activated Adjacent Track Erasure (ATE) for a specific write head. The write head had a rectangular main pole of 13 by 40 nm (cross-track x down-track) with pole trailing shield gap of 5 nm and pole side shield gap of 10 nm. The distance from the pole to the top surface of the medium was 5 nm, the medium was 10 nm thick and there was a 2 nm interlayer between the soft underlayer (SUL) and the medium, making a total SUL to pole spacing of 17 nm. The results showed that ATE would be a major problem and that cross-track head field gradients need to be more tightly controlled than down-track. With the write head used, recording at 1 Tb/in² would be possible on single domain islands.
Supervisor: Miles, James Sponsor: EPSRC ; School of Computer Science
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Data Storage ; Bit Patterned Media ; Write Errors ; Statistical Model ; Nano-Island Magnetic Materials ; Magnetometric Demagnetising Factors