BRUNN, O. Magnetické fáze umělého spinového ledu na čtvercové mřížce [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2019.

Posudek vedoucího

Rougemaille, Nicolas

First, it is important to note that the diploma thesis was entirely prepared at the Brno University of Technology, while I work at the Néel Institute in Grenoble, France. All the scientifc discussions I had with Ondřej Brunn were done through Skype meetings. Besides, we only briefy discussed together the content of the manuscript and what is presented here is the result of his own understanding of the topic. The manuscript thus refects quite well his overall contribution to the project, although there is signifcantly more measurements and analyzed data than suggested at frst sight when reading the manuscript. The topic presented in this diploma thesis is the continuation of the Master internship Ondřej Brunn did in our lab last year through an ERASMUS exchange program (Feb 2018 – July 2018). The experimental measurements (magnetic force microscopy) showing magnetic images of various square arrays of interacting nanomagnets were obtained at that time, when Ondřej Brunn was working in our group. During the diploma thesis, he essentially analyzed those measurements, performing complementary micromagnetic simulations started during his ERASMUS stay, and further improving an own-made Matlab script (also frst developed during the ERASMUS internship) to semi-automatically extract relevant information from the magnetic images. Although this work combines his diploma thesis and his ERASMUS stay at Néel, Ondřej Brunn handled all aspects of the project, from the sample design to its characterization (atomic force microscopy and scanning electron microscopy), investigation (demagnetization protocol, magnetic force microscopy), simulation (using an open source micromagnetic code), and analysis (image processing). Overall, the work presented in the diploma thesis provides suffcient materials for a publication. In particular, Ondřej Brunn produced and analyzed a very large amount of data, especially to check the reproducibility of the results, to identify potential artifacts from the lithography, to test several hypotheses and to improve the statistics of the measurements. In my opinion, all the work he provided does not appear clearly in the diploma thesis and, as presented, the manuscript could leave the impression that a few measurements only were done. This is not quite true and I was impressed by the amount of data he generated and the quality of the output. Finally, Ondřej Brunn is a well-organized and pleasant person to work with. I really appreciated interacting with him. Our collaboration will continue this fall in the framework of a PhD thesis for which he successfully got a cotutelle grant.

Posudek oponenta

Hrabec, Aleš

The Master thesis by Bc. Ondrej Brunn deals with the experimental realization of a new geometry of square artificial spin ice system built by magnetic monodomain blocks. The thesis is written in English language and apart from a few typos (which were communicated separately) is written on a high level. The text is clearly written and the background knowledge of the physics of the frustrated systems is gradually built up throughout the introduction. This is done in such a way that the motivation for the development of a new artificial spin ice system naturally comes up. The new system, composed of distorted square lattice, is studied experimentally and also modeled micromagnetically using a commercially available code. The comparison, although indirect, between the experimental data presented in Figs. 4.7 and the numerically calculated data shown in Fig. 4.3 is remarkable. I also particularly appreciate the demonstration of the lithography quality on the vertex population presented in Fig. 4.14. A clear degradation of the expected physics is shown with the poorer lithography. The master thesis fulfils expectation of a complex and systematic work and I can only recommend this inspiring work to be defended in front of the committee.

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