The ferromagnetic semiconductor gallium manganese arsenide is an important test-bed material for spintronics applications. Whilst a Curie temperature anywhere close to room temperature has yet to be demonstrated, the excellent micromagnetic properties, simple band structure and unusual combination of having both low moment densities and high spin-orbit coupling make this an interesting material to study from both theoretical and experimental perspectives. This thesis reports some experimental studies into the magnetic and magnetoresistive anisotropies in gallium manganese arsenide. In the first main chapter a study of the Anisotropic Magnetoresistance in thin (Ga,Mn)As films is reported, based on transport measurements of micro-scale devices, contributing to the first systematic study in this material. The Anisotropic Magnetoresistance comprises crystalline and non-crystalline components; this study shows that a uniaxial crystalline component can dominate over the whole range of temperatures from 2K up to the Curie temperature, the first time this has been seen in any material system to our knowledge. The following chapter shows that the magnetic anisotropy of gallium manganese arsenide thin films can be engineered by lithographically patterning the material into structures on length scales of a micron or less. Using electron beam lithography to define the structures and SQUID magnetometery to study the resulting magnetic configuration, it is shown that the magnetic anisotropy can be greatly modified, even resulting in a switching of the easy- and hard-axis directions. Finally a new technique based on Anisotropic Magnetoresistance measurements is presented to locate the crossover of competing magnetic anisotropy coefficients in the temperature domain. Conventionally performed by SQUID magnetometry, this new technique is cheaper and simpler whilst qualitatively reproducing the main features of the SQUID measurements.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:514719 |
| Date | January 2008 |
| Creators | King, Christopher Stuart |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/10646/ |
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