A detailed experimental study using magnetooptics has been performed into magnetic switching and domain structure predominantly in high quality ultrathin epitaxial Ag/Fe/Ag(001) films, for both in-plane and out of plane magnetisation. When the magnetisation is in-plane, magnetic switching has been found to proceed by a series of irreversible jumps of the magnetisation direction, each of which is mediated by the sweeping of domain walls. A simple phenomenological model has been developed which explains the switching and which highlights the role of magnetic anistropy and domain wall pinning by defects. Further micromagnetic modelling, combined with experiments, showed that the defects which determine coercivity are atomic steps on the Fe surface (named 'micropins'). A series of time resolved studies revealed that in addition to the micropins there also exists a second domain wall pinning mechanism, named 'macropinning' which is due to extrinsic defects such as scratches and other surface damage and which is not primarily responsible for coercivity. It has been found possible to engineer artificially the magnetic properties of a Permalloy film by introducing controlled macropins through lithographic structuring. The interplay between dipolar effects and intrinsic anisotropy leads to a novel domain structure during switching which could have important technological applications. In contrast to the in-plane magnetised case, in which the domain structure is an interim state which mediates the magnetic switching, the out of plane magnetised system was found to adopt a domain structure as its preferred ground state for certain temperatures and film thicknesses. These have been described by a magnetic phase diagram.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598084 |
| Date | January 1997 |
| Creators | Cowburn, R. P. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.002 seconds