Micromagnetic simulations of maghemite nanospheres in FCC arrays

Alkadour, Bassel (2015) Micromagnetic simulations of maghemite nanospheres in FCC arrays. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (3MB)

Abstract

Encouraged by recent developments in synthesizing magnetic nanospheres and nanos- phere super-lattices, we study maghemite nanospheres using stochastic LLG implemented by Maglua programming environment. We consider core-shell model where the core has bulk like exchange and the surface has weak exchange and radial anisotropy. First, we study noninteractiong nanospheres with diameters ranging from 5 nm to 7.5 nm. For comparison, we vary the surface anisotropy and the surface thickness. We observe ferrimagnetic order where the core has a bulk-like spin texture and ordering temperature whereas the surface spins show a hedgehog-like texture with a domain wall at the magnetic equator. The nanospheres prefer the magnetic moment to be in the direction that maximizes the surface vacancies at the equator, which results in a magnetic torque. Also, results of multi-scale simulations of 7.5 nm maghemite nanosphere FCC arrays with different surface thicknesses are presented. Comparing these arrays with the corresponding dipole arrays (with no anisotropy) reveals an orientational disorder below T = 20 K due to magnetic torque generated by the surface vacancies.

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