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Title: Role of morphology in ultrathin magnetic Fe films
Author: Freeland, D. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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Single crystal ultrathin Fe films have been grown on Ag(100), GaAs(100) and InAs(100) substrates, using MBE. As magnetic properties are highly dependent on the interface and morphology of surfaces, characterisation have been performed in-situ, to establish the correlation between magnetism and morphology. Epitaxial Fe has been deposited on GaAs(100)-4x6 at room temperature and the evolution of the phase transition from superparamagnetic to ferromagnetic has been studied. MOKE measurements indicate that after the onset of ferromagnetism, the whole Fe film is ferromagnetic and there are essentially no magnetically dead layers. This is in contrast with previous studies and indicates that, under certain conditions, the growth of Fe/GaAs(100) may not be complicated by interface alloying to the extent as previously thought. Whilst the lattice mismatch between Fe and InAs(100) is far greater than that for GaAs(100), epitaxial bcc Fe has been stabilised on InAs(100)-4x2. This system holds much promise for magneto-electronics since, unlike GaAs, InAs forms an ohmic contact with Fe. A uniaxial anisotropy has been observed in ultrathin, 5-10 ML Fe/InAs(100), grown at room temperature, with easy axis along [011]. This is in contrast to the far stronger uniaxial anisotropy in Fe/GaAs(100), whose easy axis is along the [01‾1] direction. Possible explanations for the differences between these systems are discussed. RHEED studies on Fe/InAs(100) have shown that there is a significant morphological relaxation, in the ultrathin 5-25 ML Fe region. Furthermore, relaxation occurs more rapidly along [01‾1] than along [011] - this 'anisotropic lattice relaxation' suggests magneto-elastic effects. LEED spotwidth measurements for Fe/Ag(001), indicate that there are two changes in surface morphology within the first seven monolayers of Fe growth. The coercivity thickness dependence is directly compared with LEED and discussed in terms of domain wall pinning at interfaces. Factors such as island growth, interdiffusion and segregation are highlighted to explain these structural and magnetic properties.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available