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Title: Exchange anisotropy in magnetic thin films
Author: Bali, R.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2009
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I have studied Exchange Bias in epitaxial α-Fe2O3 and polycrystalline FeMn and CoMn antiferromagnets coupled to the ferromagnet Permalloy (Ni81Fe19). Despite the nominal magnetocrystalline anisotropy of Permalloy, surface features such as vicinal steps and roughness induced strong uniaxial anisotropy. Exchange coupling with epitaxial α-Fe2O3 led to a biaxial anisotropy component in the ferromagnet. Anisotropy axes of the biaxial component remained fixed despite applying magnetic field at elevated temperatures. The magnitude of biaxial anisotropy varied with every temperature cycle, providing implicit evidence of domains in the antiferromagnet. In polycrystalline systems, uniaxial anisotropy of the ferromagnet set-up during growth competes with exchange anisotropy. By setting up an AF/F/AF trilayer, magnetic field cooling allowed control of the net anisotropy. These findings demonstrate that the two crucial factors that impact exchange biased thin films are (1) uniaxial anisotropies in the ferromagnet from surface and growth conditions and (2) exchange coupling with domains in the antiferromagnet. Competing effect of these two factors is the key to understanding any exchange coupled system.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available