Martina Ondříšková prepared her diploma thesis under my supervision, through a long-standing international collaboration (I supervised the diploma and PhD theses of several other BUT students -- Vojtěch Schánilec, Ondřej Brunn and Marek Zálešák --). Her work was the continuation of a six month Erasmus research project she prepared at the Néel Institute last year. Her project is related to the investigation of the exotic, many-body physics which occurs in magnetically frustrated two-dimensional spin lattices under specific boundary conditions. In particular, she was in charge of fabricating, imaging and analyzing magnetic configurations obtained after field demagnetizing lithographically-made arrays of interacting nanomagnets, arranged on the so-called square ice geometry.

Martina Ondříšková demonstrated professional research skills in the field of artificial frustrated magnetism. She conducted a large amount of magnetic imaging experiments using magnetic force microscopy and run different numerical codes already developed in the group to extract relevant physical quantities. She also successfully fabricated a set of working samples, sometimes requiring difficult to reach specifications. Martina Ondříšková is a serious, rigorous, hard working young scientist. Based on the work she produced, we envision the publication of an article in an international peer-review journal.

Report on the manuscript submitted by Martina Ondříšková to obtain a Master from BRNO University of Technology
 

Martina Ondříšková carried out her Master internship work both at the Néel Institute in Grenoble and at the Institute of Scientific Instruments of the Czech Academy of Sciences under the supervision of Dr. Nicolas Rougemaille.

The aim of her work was to study the physics of arctic circle in artificial square-ice magnets. The manuscript is divided into three parts: a chapter describing the scientific context, another covering the methodologies used and a final chapter presenting the experimental part of the work undertaken.

The whole report is well written and contains elaborate, neat figures, making it a pleasure to read. I regret only a few repetitions that could have been avoided. This in no way detracts from the quality of the work reported!

The introduction does an excellent job of establishing the broader context of geometrical frustration in artificial spin systems, emphasizing the importance of studying these meta-materials and the clear motivation behind this research project.

Secondly, the methodology section is well detailed. All the aspects needed to understand the following section are dealt with clearly and precisely.

The third and final chapter contains two important sub-sections. The first sub-section presents the results of the manufacturing process and describes the search for winning design rules, which are subsequently adopted. The second sub-section is devoted to both a presentation and a detailed analysis of the results obtained. The results obtained here are quite original and very convincing. As well as paving the way for promising studies on artificial square-ice magnets, these results de facto define a new state of the art!

To conclude this report, I'd like to say that I was very impressed by the quantity and quality of the work done. The production of samples of this type is not an easy task and Mrs Ondříšková was able to obtain high quality samples. In addition to that, this study unequivocally shows that the right boundary conditions are in place to explore the properties of the arctic circle physics in artificial square-ice magnets. Several properties of these systems are reported here for the first time in the case of artificial square-ice magnets. Finally, it is clear from this report that Mrs Ondříšková has the skills required to successfully complete her Masters internship.

Dr. Daniel Lacour Topics for thesis defence:

1. p. 17: Is it possible to explain in few words the diamond shape imposed by the domain wall boundary conditions?
2. p. 22: With regard to the manufacturing process, which is carried out on (10×10) mm2 chips, I wonder if the thickness of the resist is uniform between the center of the chip and the edges. Has this thickness been measured and if so, how?
3. It says p25: “We can rationalize and simulate what happens during the process, but in reality, the key part when the ground state configuration is reached is an extremely fast process.” I'm not sure I understand the meaning and consequences of this sentence. Can you tell us a bit more?
4. Beyond square ice, are there other artificial spin ice systems for which it would be interesting to explore the consequences of imposing domain wal boundary conditions?
5. Beyond square ice, are there other artificial spin ice systems for which it would be interesting to explore the consequences of imposing the domain wall boundary condition ?
6. p. 38, fig. 3.6: How are the errors bar determined?