New materials for magneto-optical applications.

Radek Ješko

Doctoral thesis

Abstract:

V této disertaci byly zkoumány strukturní, optické a magnetooptické vlastnosti Heuslerových slitin, feritů a Perovskitů. Cílem práce bylo určit jejich vlastnosti a případnou vhodnost pro aplikace v magnetooptických zařízeních, jako například nereciprokých optických izolátorech, nebo ve spintronice. Dalším cílem bylo porovnat jejich změřené vlastnosti s ab-initio výpočty k vylepšení přesnosti výpočtů a následné analýze preferovaných přechodů zodpovědných za magnetooptickou aktivitu. Studované Heuslerovy slitiny obsahovaly objemový vzorek Co2FeAl0.5Si0.5 připravený pomocí obloukového tavení v ochrané atmosféře, a tenké vrstvy Rh2MnGe a Rh2MnAl připravené pomocí pulzní laserové depozice, respektive magnetronového naprašování na MgO substrátu. Dále byly studovány tenké vrstvy magnetitu (Fe3O4) připravené za pomoci epitaxe z molekulárního svazku při rozdílných tlacích reagujícího kyslíku znovu na MgO substrátu. Také byly charakterizovány vrstvy Co-ferritu připravené za pomoci dip-coatingu z roztoku jeho rozpuštěných složek, a to na skle, křemeném skle a křemíku. Posledním typem studovaných látek byly Perovskity vyrobené metodou přetavování plovoucí zóny ze slinutých prášků zdrojových oxidů neodymu, praseodymu, železa a manganu, a to ve stechiometriích NdMn(1-x)Fe(x)O3 a PrMn(1-x)Fe(x)O3, kde hodnota x náleží do rozmezí 0 …moreless

Abstract:

In this doctoral thesis, structural, optical, and magneto-optical properties of Heusler compounds, ferrites, and Perovskites were investigated. The aim of the work was to determine their properties and possible suitability for the applications in magneto-optical devices, such as the non-reciprocal optical insulators, or in spintronic devices. Another goal was to compare their measured properties with ab-initio results to improve the accuracy of the first principle calculations and then analyze the preferred transitions responsible for magneto-optical activity. The Heusler compound materials studied contained a bulk sample of Co2FeAl0.5Si0.5 prepared by arc melting in protective atmosphere and a thin film of Rh2MnGe and Rh2MnAl prepared using pulsed laser deposition and magnetron sputtering, respectively, on MgO substrate. Next studied were the thin films of magnetite (Fe3O4) prepared by molecular beam epitaxy at different reactive oxygen pressures again on MgO substrate. Co-ferrite layers prepared by dip-coating from a solution of dissolved compounds and subsequent annealing prepared on glass, quartz glass, and silicon were also characterized. The last type of the studied compounds were the Perovskites made by floating zone remelting of sintered powders of source oxides of neodymium, praseodymium, iron, and manganese. These samples were made in stoichiometries of NdMn(1-x)Fe(x)O3 and PrMn(1-x)Fe(x)O3, where x is between 0 and 1. Of the produced volume orthorhombic Perovskites, however, we included the results only for NdFeO3, which so far has been the only one with measurable magneto-optical effect at room temperature. For all presented samples their optical properties were determined by spectroscopic ellipsometry. Magneto-optical properties were obtained using apparatuses for measuring the spectroscopic Kerr effect in reflection either in a polar or longitudinal configuration. For the first time we also present the results of spectroscopic quadratic Kerr effect on magnetite samples. A detailed comparison of the measured properties with ab-initio calculations is presented for Heusler's compound Co2FeAl0.5Si0.5. This material showed the highest magneto-optical effect from the ones we have measured and is one of the materials of particular interest in spintronics thanks to its use as a half-metallic ferromagnet in spintronic filters and tunneling magnetic junctions, in which it shows abnormally high spin polarization even at room temperature. However, our results indicate that it is not a true half-metal at room temperature.

Keywords

Magnetooptický Kerrův jev, kvadratický Kerrův jev, Elipsometrie, Heuslerovy slitiny, Perovskity, Magnetit, Co-ferit, Polokov

Keywords

Magneto-optical Kerr effect, QMOKE, Ellipsometry, Heusler compounds, Perovskites, Magnetite, Co-ferrite, Half-metal

Language used: English

Date on which the thesis was submitted / produced: 20. 8. 2019

Thesis defence

• Date of defence: 5. 11. 2019
• Supervisor: Jaroslav Hamrle
• Reader: Petr Kužel, Miroslav Kučera, Tomáš Ostatnický

VŠB - Technical University of Ostrava

Univerzitní studijní programy

Doctoral programme / field:
Nanotechnologie / Nanotechnologie