ZÁLEŠÁK, M. Umělé magnety ledu Shakti: degenerace základního stavu, Coulombova fáze a monopólové excitace [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2023.

Posudek vedoucího

Rougemaille, Nicolas

Verbal classification: Marek demonstrated professional ability in the field of artificial frustrated magnetism. He conducted a substantial amount of magnetic imaging experiments using magnetic force microscopy and run different numerical codes to extract relevant physical quantities. Marek is a serious, rigorous, hard working young scientist. We envision the publication of two articles in peer-review journals.

Posudek oponenta

Hrabec, Aleš

The master thesis of Bc. Marek Zalesak deals with the investigation of the artificial spin system based on the shakti geometry. This geometry was originally proposed by Chern et al. and further experimentally realized by Gilbert et al. Both authors showed how the Shakti spin configuration can be mapped onto a classic square spin ice, which then showed desired properties. The aim of this work was to revisit the experimental realization of this particular lattice and analyze the data in a more elaborate way, as was shown recently by Vojtech Schanilec. From the experimental point of view, the Gilbert’s results were reproduced although with a slightly less powerful demagnetization protocol. The deeper analysis of the data reveals that the underlying physics imprinted into the magnetic ordering is more complicated than previously reported by Gilbert and colleagues. The data were then analysed to identify all the vertex populations, which were then confronted with the Monte Carlo simulations. This was also confirmed by comparing the experimental and computed magnetic structure factors. The Monte Carlo model was then modified in order to reproduce the experimental data. In the final, but important, sections, it is concluded that also the mapping itself also brings some significant restrictions. I personally find the work original and scientifically sound going beyond the groundbreaking work of Gilbert. The work is very mature containing all the key scientific ingredients: critical analysis of the literature, transparent data analysis and its critical evaluation. I am actually excited that one can reproduce the published data, which is something of great significance and which is rarely reported. It is also very transparent how the previous data were analysed and what the overlooked points were. The amount of experimental data and statistics is certainly sufficient to draw the well-supported conclusions. Mr. Zalesak also performed an extensive analysis of the Monte Carlo simulations, which were performed by the team at Neel Institute in Grenoble. The content of the manuscript is suitable and it contains all the necessary background to understand the experimental findings and the analysis. One weaker point is that sometimes it is slightly hard-to-follow some of the English expressions, which make some parts harder to understand. Nevertheless, the thesis as a whole is written at a very good level and I am looking forward to seeing this being published in a peer-reviewed journal. I am certainly in favor to recommend this nice work to be defended in front of the examination committee.

eVSKP id 149399