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Write Errors in Exchange Coupled Bit Patterned Media

Talbot, Jennifer Esther

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

The fabrication of Bit Patterned Media has become highly developed, with samples fabricated of over 1.5 Tb/in2. However, writing BPM presents signiﬁcant challenges and for a system to be developed studies must be made into writing. This work has investigated a number of effects on the writing of Bit Pattterned Media (BPM). Magnetostatic interactions between islands have been used to investigate the effect of patterns of magnetisation on the write-window of a BPM system. A method of acquiring a distribution of patterns was determined and used to vary the probability of a target island switching. This showed that magnetostatic interactions between islands could be modelled as a variation in the anisotropy ﬁeld. The relationship between island parameter distributions, the write-window and error rates was also explored. The effect of non-Gaussian distributions on the error in a BPM system was studied. It was concluded that tails of island parameter distributions have a signiﬁcant effect on errors occurring in the write process of a BPM system. Therefore an accurate distribution of island parameters must be known and the necessary accuracy of such a distribution was established. Furthermore a model of BPM writing where the shape of the head ﬁeld is approximated from the value at the maximum head ﬁeld gradient will not account for switching in the tail of a real head ﬁeld. This led onto a study of the ideal write point in BPM. In conventional recording theory the medium is designed to switch when the applied head ﬁeld is at the position of its maximum gradient, which produces sharp transitions between magnetisation regions. A natural assumption in BPM is that the system could be optimised by setting the island switching ﬁeld in a similar manner. This strategy of optimisation was investigated to see what gives the minimum error, or maximum write-window. It was concluded that optimisation could not be solely based on the maximum head ﬁeld gradient, furthermore assuming the shape of the head ﬁeld from this point will not produce an accurate estimation of the error in a BPM system.