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Bachelor's Thesis
Author of thesis: Bc. Sára Hrdinová
Acad. year: 2023/2024
Supervisor: Ing. Oleksii Zadorozhnii
Reviewer: Ing. Mgr. Peter Kepič
An equiatomic alloy FeRh exhibits a phase transition from antiferromagnetic to ferromagnetic ordering at a temperature about 350 K. This makes it an ideal material for studying exchange interactions between ferromagnetic and antiferromagnetic ordering within a single material system. In this work, we investigate the relaxation of the compressive epitaxial strain caused by nanopatterning of the FeRh film. Relaxation of this strain leads to the stabilization of the ferromagnetic phase, which could lead to the formation of a suitable interface between the relaxed ferromagnetic nanostripe and the compressed antiferromagnetic film. In this bachelor thesis we first describe in detail the magnetic properties of the materials and properties of the FeRh alloy with the emphasis on the phase transformation. Our experiments supported by recent literature research include depositing FeRh layers with thicknesses of 36 nm and 180 nm. After patterning by electron beam lithography, the samples were characterised using Magnetic Force Microscopy. These measurements show that the strain relaxation is strongly dependent on the orientation of the nanostripe with respect to the crystal structure of the substrate. For an orientation of 0°, the strain relaxation is more pronounced than for 45°. The 36 nm thin FeRh layers do not form a continuous phase boundary between the nanostripe and the full film in 1000 nm wide nanostripes. Instead, they form small domains that are indicative of the strain distribution in the structure. Layers of 180 nm thickness show a phase coexistence between the nanopatterned stripe and the film for stripes longer than 25 µm. Well-defined interfaces have been achieved for stripe widths from 1250 nm to 300 nm. For structures with wider stripes, the ferromagnetic phase at the edges of the continuous layer merges with the ferromagnetic phase in the nanostripe, thereby curving the interface. This merging is gradually broken at the interface in the thinner stripe with dimensions 800 nm and 600 nm. The stripe of width 300 nm shows a clear interface between its sides.
Ferromagnetism, Antiferromagnetism, FeRh alloy, Phase transition, Epitaxial strain, Magnetic, Force Microscopy, MFM, Strain-induced phase transition
Date of defence
13.06.2024
Result of the defence
Defended (thesis was successfully defended)
Grading
A
Process of defence
Po otázkách oponenta bylo dále diskutováno: Srovnání MFM a AFM z hlediska interakčního potenciálu vzorek-hrot. Studentka na otázky odpověděla.
Language of thesis
English
Faculty
Fakulta strojního inženýrství
Department
Institute of Physical Engineering
Study programme
Physical Engineering and Nanotechnology (B-FIN-P)
Composition of Committee
prof. RNDr. Tomáš Šikola, CSc. (předseda) prof. RNDr. Jiří Spousta, Ph.D. (místopředseda) prof. RNDr. Radim Chmelík, Ph.D. (člen) prof. RNDr. Petr Dub, CSc. (člen) prof. Ing. Jan Čechal, Ph.D. (člen) prof. Ing. Miroslav Kolíbal, Ph.D. (člen) doc. Mgr. Vlastimil Křápek, Ph.D. (člen) doc. Ing. Stanislav Průša, Ph.D. (člen) doc. Ing. Radek Kalousek, Ph.D. (člen) doc. Ing. Miroslav Bartošík, Ph.D. (člen) RNDr. Antonín Fejfar, CSc. (člen)
Supervisor’s reportIng. Oleksii Zadorozhnii
Grade proposed by supervisor: A
Reviewer’s reportIng. Mgr. Peter Kepič
Grade proposed by reviewer: B
Responsibility: Mgr. et Mgr. Hana Odstrčilová