This thesis contains data from micromagnetic simulations that investigate new methods for data storage and processing on the nanoscale using ferromagnetic nanowires. First I consider a magnetic memory, domain wall trap memory, which could compete with a number of existing devices that are currently in widespread use. Domain wall trap memory exhibits a 90% lower coercivity over traditional MRAM designs because, instead of remagnetizing a rectangular or oval magnetic free layer by moment rotation or domain nucleation, an existing domain wall is moved along a structured nanowire to remagnetize part of the wire. I determine the fields for de-pinning, switching and expulsion of domain walls in memory cells to show that the margins between them can be sufficiently large for reliable operation. The nudged elastic band method is used to show that domain wall trap memory is thermally stable at room temperature.

Συστήματα μαγνητικών ταινιών χρησιμοποιούνται ευρέως ως μέσα αποθήκευσης και αποκατάστασης δεδομένων. Λόγω του χαμηλού τους κόστους αναλογικά των σκληρών δίσκων συνεχίζουν να προτιμούνται σε μεγάλο πλήθος εφαρμογών όπως δευτερεύουσες συσκευές αποθήκευσης, εγγραφής και επεξεργασίας ηχητικών δεδομένων,βιντεοκάμερες κ.ά. Σε περιπτώσεις όπου θέλουμε να επεξεργαστούμε μια μαγνητοταινία για γρήγορη μεταφορά ή εγγραφή δεδομένων θα πρέπει -η ταινία- να μεταφέρεται σε υψηλή ταχύτητα από το μηχανισμό του συστήματος. Η ταχύτητα αυτή να διατηρείται σταθερή και να βρίσκεται σε συγχρονισμό ε την κεφαλή ανάγνωσης/εγγραφής προς αποφυγή σφαλμάτων μεταφοράς και αναγνώρισης δεδομένων, αναπηδήσεων και χρονικών σφαλμάτων. Σε πιθανά σφάλματα η επαναφορά της ταινίας στο επιθυμητό σημείο αποτελεί τη λύση για την αποκατάσταση του σφάλματος. Η επιτάχυνση και επιβράδυνση που δέχεται η ταινία σε κάθε γρήγορη αναζήτηση δεδομένων προκαλούν τη μεγαλύτερη επιβάρυνση σε αυτή. Ειδικά η συχνή επανατοποθέτηση της ταινίας στο ίδιο ση είο λόγω της βαθμιαίας εξασθένισης του σήματος ανάγνωσης. Σκοπός είναι ο σχεδιασμός ενός μηχανισμού εταφοράς της ταινίας ο οποίος προσφέρει μια ικανοποιητική τάση στην ταινία όπως και ταχύτητα μεταφοράς αυτής. / Optimal control and estimation of a magnetic tape-drive system.

Bit-Patterned Media (BPM) has been recognised as one of the candidate technologies to achieve an areal density beyond 1Tb/in2 by fabricating single-domain islands out of continuous magnetic media. Though much attention has been focused on the fabrication of BPM, existing lithography techniques demonstrate difficulties in producing uniform islands over large areas cost effectively; the resulting fabricated islands often vary in position and size. The primary purpose of the research documented in this thesis is to investigate the issue of island geometry variations on the data recovery process from a perpendicular patterned media with head and media configurations optimised to achieve an areal density of 1Tb/in2. In order to achieve the research aim, a read channel model has been implemented as a platform to evaluate the read channel performance numerically. It can be also altered to investigate new read channel designs. The simulated results demonstrate that island geometry variations have a detrimental effect on read channel performance. It has shown that a BPM system can be tolerant to island position variations, but more effort needs to be paid to the effect that island size variations have on the read channel performance. A new read channel design revolving around the design of a modified trellis has been proposed for use in the Viterbi detector in order to combat the effect of island geometry variations. The modified trellis for island position variations results in extra states and branches compared to the standard trellis, while the modified trellis for island size variations results in only extra branches. The novel read channel designs demonstrate an improved read channel performance in the presence of island geometry variations even with increasing amounts of island position and size variations. There are two ways to obtain the read channel performance in terms of the bit-error-rate (BER): a) by running a numerical Monte-Carlo simulation to count the number of bits in error at the output of the read channel model and b) using an analytical approach to calculate the BER by approximating the noise into a known distribution. It is shown that both ways demonstrate very similar results, which indicates as long as the distribution of the noise present in read channel model is predictable, the analytical approach can evaluate the BER performance more efficiently, especially when the BER is low. However, the Monte-Carlo simulation is still useful for understanding of the correlation of the errors. Novel trellis proposed in this work will contribute to the commercial development of BPM in two ways: a) to improve the data recovery process in BPM systems, b) to allow a tolerance of 10% size variations for the existing fabrication techniques.