A new type of magnetic microscopy is described: Real-Time Scanning Kerr Microscopy (RTSKM) uses high bandwidth detectors to study single-shot magnetisation reversal events without averaging or stroboscopic techniques. The advantages of RTSKM are localised measurements of magnetisation, compatibility with high applied fields and ability to extract statistical details of reversal. These advantages are constructed with current dynamic magnetic microscopies. The details of the development of the equipment are presented: 100 MHz brandwidth photodetectors of sufficient sensitivity, swept field source capable of providing 3 . 10<sup>6</sup> Oes<sup>-1</sup> and data representations to cope with the large volume of data. A fitting procedure is described that extracts parameters from single-shot RTSKM measurements that characterise the reversal. Distributions of these parameters gives valuable information on the stochastic nature of reversal. Measurements made of continuous Fe (15 nm)/GaAs films for slow field sweep rates are presented. A measurement of the domain wall velocity is calculated from a transit time measurement and compared with the values obtained directly from the dynamic MOKE data. Other domain wall phenomena are observed and discussed. The measurements show the need for statistical measurements on domain wall motion. Results are also presented of Fe(15nm)/GaAs film that was patterned into 50 mm circular dots. This sample was also studied at low field sweep rates. An inhomogeneous switching mechanism is found which is not fully explained. The switching mechanism proceeds via three stages, each of which is associated with a different region of the dot. The different regions are analysed separately and different domain wall dynamics are found.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:599309 |
| Date | January 2002 |
| Creators | Gardiner, S. M. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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