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Magnetooptical and magnetotransport effects in non-collinear antiferromagnets
Baďura, Antonín ; Schmoranzerová, Eva (advisor) ; Janda, Tomáš (referee)
In this thesis, we investigate the magnetic properties of an antiferromagnet Mn5Si3. Mn5Si3 shows two configurations of magnetic moments depending on temperature: the low-temperature phase (below 90 K) is noncollinear and noncoplanar, while the spin configuration is collinear at higher temperatures up to 240 K. Furthermore, the band structure of Mn5Si3 is spin-split in both antiferromagnetic phases via a specific nonrel- ativistic mechanism, referred as altermagnetism. We probed this spin-splitting by two distinct methods: Firstly, we characterized the transport properties of Mn5Si3 by mea- suring electronic and thermoelectric transport phenomena. Particularly, we detected the spontaneous Hall and Nernst responses in Mn5Si3 thin epitaxial films. The key outcome was a detailed analysis of the spontaneous Hall signal together with the observation of the spontaneous Nernst effect. In the second approach, we studied magnetooptical re- sponse of the thin films, where we focused on reflective geometry (the polar Kerr effect and the Voigt effect). We observed a pronounced signal in the Voigt geometry, which is quadratic in magnetization and could correspond to a magnetooptical signal. Further- more, we observed a change in optical response when the thin-film samples were exposed to a thermally-induced mechanical...
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Thermo-transport effects in antiferromagnets
Baďura, Antonín ; Schmoranzerová, Eva (advisor) ; Martins Godinho, João Pedro (referee)
This thesis investigates magnetic properties of an antiferromagnet Mn5Si3 in both collinear and noncollinear antiferromagnetic phases, which this compound evinces. The work is based on three distinct experimental approaches: The first one comprises mea- surements of magnetotransport phenomena (namely anisotropic magnetoresistance and Hall effects), the second one studies thermal counterparts of these effects (particularly the anomalous Nernst effect). Finally, we used scanning thermal gradient microscopy in order to observe the domain structure of Mn5Si3. The key outcome of the magnetotransport measurements is an observation of the Hall response in the collinear antiferromagnetic phase, which we attribute to the recently proposed crystal Hall effect. Furthermore, the thermotransport measurements resulted in the first observation of the anomalous Nernst effect in this compound. Due to the variety of artefacts, we did not record any convincing image of the domain structure in Mn5Si3. The analysis of the artefacts was supported by mathematical modelling that helped to pinpoint their origin.
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