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Magnetoelasticity and Optically Induced Magnonic Crystals in CoFeB and Ni

Tamming, R.R. (2017) Magnetoelasticity and Optically Induced Magnonic Crystals in CoFeB and Ni. Master's Thesis / Essay, Applied Physics.

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Multiferroics, materials that exhibit interactions between either magnetism, electricity and elasticity, show great potential in future applications. One of the multiferroic materials that has gained large interest is CoFeB due to the large resistance achieved in magnetic tunnel junctions at room temperature. The focus of this research is to obtain a better understanding of the spin dynamics by using the magnetoelastic interaction of CoFeB and compare it with the results previously found for Ni samples. The experiments performed used an all-optical pump-probe setup, com- bined with a Faraday detection scheme to measure the change in polariza- tion of the probe pulse. The setup is capable of introducing a second pump pulse, simultaneously with the first one, to create acoustic waves in the sample. Whilst doing this, an external magnetic field is applied, capable of rotating in-plane of the sample. The results entails two parts of which the first is the determination of the magnetic anisotropic properties of CoFeB on SiOx and MgO substrates by using the single pump-probe setup. Both of the samples exhibit uni- axial anisotropy which is more prominent in the MgO sample. The origin of the anisotropy remains unknown, however, magnetic fields are present during the fabrication which might induce magnetic ordering of the sample. For the second part, the second pump is introduced. Via magnetoelastic interaction, spin precession is driven in both the CoFeB and the Ni sample at the resonant frequencies of the acoustic waves and the larmor precession. When rotating the magnetic field, the total signal shows un- expected behaviour. Whereas the magnetoelastic interaction predicts a sin(2φ) relation for the precession signal, the obtained signal for CoFeB disappears mostly after 30◦. For Ni, there is a dip in the signal at 32◦. The introduction of magnonic crystals and spin wave localization is made to explain this phenomenon, however, more research is required to get a full understanding.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Applied Physics
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:30
Last Modified: 15 Feb 2018 08:30

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