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A Study of Thin Magnetic Films of Iron Oxides and Yttrium Iron Garnet

Zaki, Aliaa (2018) A Study of Thin Magnetic Films of Iron Oxides and Yttrium Iron Garnet. PhD thesis, University of Sheffield.

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Abstract

The structural, magnetic and magneto-optical properties of iron oxides (wustite, magnetite, Hematite and maghemite), yttrium iron garnet (YIG) and calcium doped YIG (Ca:YIG) thin films prepared by pulsed laser deposition (PLD) technique were studied. The properties of iron oxides films grown on sapphire substrate were found to be dependent on the annealing temperature of the target and the oxygen pressure (PO2) during the ablation. For example, the high annealing temperature of the target and base pressure give wustite, whereas a lower annealing temperature with same oxygen pressure and conditions give magnetite. In addition, the fraction of Fe3+ ions increases with increasing the oxygen pressure, which leads to pure maghemite at PO2 more than 100 mTorr. YIG thin films were grown on gadolinium gallium garnet (GGG) and yttrium aluminium garnet (YAG) substrates. The GGG substrate was found to cause a lower lattice strain (ɛ= 0.016%) in YIG lattice compared to YAG substrates (ɛ=1.12%). The oxygen pressure was also found to affect the magnetic and magneto optical properties of YIG thin films. For example, YIG/GGG films prepared at PO2 =400 mTorr were found to have magnetic properties close to bulk YIG with saturation magnetisation (Ms= 143 emu/cm3) and coercive field (Hc) <1 Oe. These insights were used to prepare Ca:YIG thin films. The Ca:YIG films showed an increase in the oxygen vacancies, a decrease in Ms and high strain; with increasing the amount of doped Ca+2 ion. It also found that all the Ca:YIG/GGG films contain about 5% Fe2+ at this PO2. For example, the film that contains x=0.05 has a reduction in the magnetisation of about 18% from the pure YIG/GGG thin film. Lower PO2 led to the occurrence of Fe2+ ions in the tetrahedral sites of YIG and increased the oxygen vacancies that reduced Ms.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > Physics and Astronomy (Sheffield)
Depositing User: Mrs Aliaa Zaki
Date Deposited: 23 Oct 2018 15:05
Last Modified: 23 Oct 2018 15:05
URI: http://etheses.whiterose.ac.uk/id/eprint/21664

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