Academic Awards 2023 booklet

69 Herewith the jury of the committee “Best PhD thesis of Eindhoven University of Technology 2022” would like to propose to award this prize to DR. YOURI LOUIS WINANDUS VAN HEES This PhD work was part of a large Zwaartekracht program; Research center for Integrated Photonics at the TU/e between the departments EE and APSE. In this context Youri’s endeavor focused on the fundamentals of a so-called Cobalt-Gadolinium based synthetic ferrimagnetic that has the promise to be used as a very energy-efficient memory element in integrated photonic circuits. His timing was perfect as it was just demonstrated that the magnetic orientation of a nanomagnet made from this material can be ‘switched’ (reversal of North and South pole) by merely firing ultrashort femtosecond light pulses at it, a phenomenon called ‘All-Optical Switching’ (AOS). It has the potential to create ICT devices that operate orders of magnitude faster than state-of-the-art electronic ones, at just a fraction of the current energy dissipation. In this rapidly developing field, Youri performed fundamental research, exploring novel concepts, performed hands-on experiments and always with an eye on future applications. In this way, he is a role-model for TU/e’s engineer of the future. Youri explored the possibility to combine two recently discovered phenomena to write magnetic information in a hybrid opto-magnetic racetrack. The first phenomenon, AOS, is all about a fundamental concept in physics, i.e., exchange of angular momentum via the electron ‘spins’ (electronic magnetic moments) between the Co and Gd layer. To harvest the second phenomenon, Youri designed and fabricated a clever sample structure in which an additional set of layers was added, which inject an ultrashort ‘spin current’ when illuminated by the same laser pulse that switched the Co/Gd. This adds an additional source of angular momentum that can compete with local exchange of angular momentum at the Co-Gd interface. Altogether, exploiting these two sophisticated phenomena, AOS and optically-induced spin currents, Youri successfully addressed a couple of hitherto unexplored bottlenecks for the hybrid technology. His work was published in a total of 9 Research papers in leading international journals during his PhD, including a publication in Nature. It is very much appreciated that Youri is able to present a highly technical topic in a very accessible way, using appropriate visual aids to effectively communicate his messages. This also sets a good example of a PhD thesis at TU/e. REPORT OF THE JURY