Author: Marco Hoffman

Technology and Sustainability – Symbiosis or Rivalry?

This was the title of the interdisciplinary discussion shared with high school students during my last outreach event just before the christmas vacation on December 18. Initiated and co-organized by my former philosophy teacher from high school, I was delighted to be invited as a speaker and discussion partner to the “Bildungsforum Schule” (educational panel in school) at the high school “Gymnasium an der Hönne” in Menden, Germany. This panel connects high school students with representatives of different fields, such as politics, media, and science to stimulate discussions and exchange.

During this event, I presented the basics of my research, its applications for industry and society as well as my voluntary work in the students’ association “Sustainability Week Zurich” to the broad audience comprising pupils, teachers, and interested local people who got to know about this event by the local newspaper’s announcement. Subsequently, highly engaged pupils asked questions about my research and moderated a discussion about the ambivalent consequences of technological progress and their interplay with different entities such as science, industry, individuals, society, and politics.

What follows, is a rough sketch of some key points that were addressed during this discussion: Transparent and comprehensible communication of the status of science, its potential and boundaries, is essential for a reasonable judgement on how to treat new developments. Several major problems, such as the sustainability and climate crisis but also general misuse of technology, seem to arise from a lack of clear responsibility allocation. Indeed, multiple entities bear responsibility for the current and future status of affairs. The technology itself is never purely good or evil, but it will always depend on the way it is utilized. Whereas it is certainly not an easy step to make every entity take their responsibility and duty seriously, open discussions like this one could help to raise awareness and contribute a (nanosized) part towards solving the challenges of our time – and if not, they can at least be an inspiring and entertaining way of exchanging and actively living democracy across different parts of society that I personally highly enjoyed.
Thus, I would like to express my sincere gratitude to Dr. Alexander Zibis, Beate Sänger, the equally motivated and well-prepared student moderators and all other involved people at the “Gymnasium an der Hönne”, Menden for making this exchange possible.

How to exploit magnets to make computers “better” in 21st century

The development and publication of artificial intelligences like OpenAI’s ChatGPT has attracted a lot of interest not only among scientists and (software) engineers but reaches deep into our diverse society. This technology provides obvious advantages but also causes undisputable issues and challenges. Next to ethical dilemmas, the tricky questions related to intellectual property and revolutionizing many jobs or making them obsolete, the immense energy consumption and corresponding emission of carbon dioxide required for training AI systems is widely discussed (Markovic et al., Nat. Rev. Phys 2, 2020).

Following Maha’s earlier blog post (“Neuromorphic Computing: A Brief Explanation” posted in December 2022, we recommend reading that one before delving into this second part) dealing with the von Neumann bottleneck and the basic functionalities of neurons and synapses, we will build up and try to exemplify in further detail, how magnetic systems can provide solutions to the imposed challenges. Therefore, the research field of spintronics tries to collaborate interdisciplenarily with researchers investigating the highly intriguing way the human brain works, and may perhaps also contribute to reducing the climate impact of this technological revolution which is on its way – for better or worse.

Conventional electronics uses „1“ and „0“ as elementary building blocks to save and compute information, also when emulating the potential in a neuron or the weight of a synapse. For instance, this implies that in order to have 32 different synaptic weight values accessible we need five elementary building blocks that can save one 1 or 0 to make up a number between 1 and 32 in the binary system. If instead we could find an alternative elementary building block, which has intrinsically 32 or more states available that is equally sized and may change its state at equal power and time scales, we could significantly improve our computing systems. Let us look at an example provided by spintronics for such an application:

A so-called domain wall separates regions with opposing magnetizations (blue and red in the image below) in a magnetic material. Such a wall can be moved by electric currents into the direction of the electrons. This implies that by using charge currents, we can change the magnetic state of the material. Now, a device can be designed such that the position of the domain wall determines the measured resistance. This is achieved by so called magnetic tunnel junctions, which we are not going to describe in further details here. As the resistance of such a device can vary between many values, depending on the position of the domain wall, we can interpret this as a synaptic weight where not only 1 and 0 but many more values are possible. Ideally, the domain wall can stop anywhere within a material making numerous states available. In real devices, such domain walls will prefer to locate around imperfections in the crystal, such as impurities („wrong atom“) or vacancies („missing atoms“). By engineering a shape geometrically to provide „prefered locations“ for such domain walls, the number of accessible state can be controlled. In the work by Leonard et al. (Adv. Electron. Mater. 2022, 8, 2200563), notches at the boundary of the magnet provide such locations. Thereby, an artificial synapse is designed that can be driven and read out at low energies and fast.

Leonard et al., Adv. Electron. Mater. 2022
Figure 1: Illustration of a notched domain wall track from Leonard et al., Adv. Electron. Mater. 2022, 8, 2200563. The blue area represents magnetization in the opposite direction as in the red area. The white vertical line is the domain wall, that can be moved by electrical currents and will get stabilized at one of the notches in equilibrium.

The location of a domain wall can also be used as a neuron potential such that this device could emulate a neuron. For this, a mechanism needs to be established that drives the wall back to one end in the absence of inputs, i.e. electric currents. One way to achieve this is by implementing a thickness gradient in the magnetic layer. Now, if a lot of currents accumulate within short enough times, the domain wall is driven across the device to the other end and the measured output value should be significantly changed only when it the wall reaches its (non-equilibrium) end. This can be engineered by the location of the read out sensors. In this way, simple magnetic devices can be used as both synapses and neurons.

Depending on the materials used in the fabrication process, the desired algorithms, energy footprint, data density and speed, various advantages and disadvantages emerge which need to be quantified and better understood and improved by spintronics researchers and engineers. It is being emphasized that conventional electronics is already performing on a high level and it poses quite a challenge to compete with that technology. Replacing conventional electronics entirely with a new system based on magnets or some other physical system, is very unlikely. However, such systems can fill gaps and perform particular subtasks in bigger computational problems, that conventional electronics are not highly suited for.

Another property of brain inspired networks that is hard to reproduce in conventional electronics is the high interconnectivity between different neuron layers. Some ten thousands of connecting synapses are typical in brains but very hard to implement in electronics.

Figure 2: Papp et al., Nat Commun 12, 6422 (2021) show how a magnetic system

Papp et al. (Nat Commun 12, 6422, 2021) therefore demonstrate how to use a magnetic system in which the magnets are by default „talking to each other“ via their magnetic interaction and train the magnetic excitations of this system (so-called spin waves, which can be imagined similar to water waves) to tell apart different spoken vowels. Roughly, this can be imagined from the figure above in the following way: We have a plane of many little magnets (imagine a pool of water that experiences waves, that can be high or low just like the the magnetization can point upward or downward) represented by each of the three squares on top of each other. On the left the vowels are injected to the system as a high-frequency signal that excites the little magnets. If that sounds too crazy, think of a boat that can drive up and down on the left boundary of the pool at low, intermediate or high speed. The level of response (intensity of resulting water waves) is illustrated by the colors. The brighter the color the more the little magnets forward the information. The magnetic system can be trained by the implementation of some „fixed guiding magnets“ to redirect the incoming signals differently depending on what signal i.e., which vowel, was input. Perhaps you may think of buoys or obstacles in the water, that redirect the water waves. Thus, brighter color can be seen in the top, center or bottom part on the right side, where the signal can be read out again at one of the three white dots. Depending on which dot received the largest signal, the system recognized a different vowel (or a different speed of the boat).

This is an example (with a highly simplifying analogy of water waves) of how magnets can solve problems in a more elegant way by exploiting the wave nature of magnets than only implementing a lot of wires/connections with the conventional electronics.

As I am aware that some parts of this post may occur confusing and not intuitive right away, please do not hesistate to reach out to me, in case that you are interested to learn more of this emerging field of spintronics: .

Intermag conference in Sendai

Taking active parts in conferences is an essential part of the scientific maturing process. Now, after my first large conference taking place in person, I can truly confirm that the discussions with various experts of the field and presentation of own research results is an inspiring and scientifically, culturally and personally enriching experience. That is why I would like to share some of my impressions gathered during the Intermag conference that took place in Sendai, Tohoku, Japan in mid-May.

It took only the time after landing to the immigration queue, until I met the first friendly faces familiar to me since the European School on Magnetism last year. In the subsequent days I catched up with many friends from Leuven, Grenoble, and Gothenburg, that I met thanks to the great exchange within the SPEAR program. Maybe even more importantly, I met many colleagues from all around the world working on very similar topics, that I was only partially aware of and I am most thankful for broadening my horizon in this regard. Lastly, meeting and talking to people that are famous within the spintronics community and whose publications I studied during the last two years was very motivating.

My own oral contribution dealt with the study on using unconventional pulse shapes employed for SOT-switching of MTJs and I am quite satisfied with the outcome, stimulating several questions that lead to more extended conversations and exchange after my talk.

Travelling and meeting people from around the world is not only about science: The Intermag organisers prepared interesting evening programs that provided us e.g. a deeper historical background knowledge of Japan and Sendai in particular, a Kimono wearing or a chopsticks crafting experience.

Everyone who knows me a bit, knows that I have a weak spot in my heart for food and for Japanese culture. Thus, you can imagine how grateful I was for the plethora of great Japanese meals I could enjoy. During my master’s degree, I had spent six months as an exchange student in Kyoto and I highly enjoyed the opportunity to again make use of my basic Japanese, visit some temples, shrines and onsens (traditional Japanese thermal baths).

Of course, during such a large conference, it is impossible to follow all interesting presentations and posters, so that now I am looking forward to the complementary online offer with recorded versions of all contributions to continue enjoying the exchange even after the in-person conference. It makes sense to exploit all advantages of online options and search for a responsible balance of online and onsite events, since large onsite conferences leave an immense carbon footprint.

To summarize, the participation in Intermag was a very valuable experience that to my perception cannot be entirely replaced by pure online formats. Science is taking place globally and for it to proceed and thrive, it needs to be discussed globally exploiting all different perspectives and insights.

NeuroSpin summer school 2022 in Lausanne

It was a great pleasure for me to co-organize the EPFL-ETH Zurich summer school “NeuroSpin school 2022: Spin based device architectures for neuromorphic computing and storage” from 22-26 August at EPFL in Lausanne.

This all-student-organized school had an active and enthusiastic participation of over 26 students from the ETH domain (EPFL, ETH Zurich, Empa, and Paul Scherrer Institut) as well as from all around Europe. The school was successful in connecting PhD students, master students and postdocs working in diverse fields from magnetism to organic electronics, machine learning and neural information processing. Despite working in different research fields, we came together with a similar vision of understanding and exploring horizons of unconventional and sustainable computing.

All participants and guest speakers of the NeuroSpin 2022 summer school in Lausanne.

We were fortunate to have guest lecturers from the backgrounds of computational neuroscience, spintronics, magnonics and artificial spin systems: Dr. Mihai Petrovici, Dr. Alice Mizrahi, Prof. Erik Folven, Dr. Naemi Leo, Dr. Kevin Garello, Dr. Aleksandr Kurenkov, Prof. Philipp Pirro, and Prof. Gyorgy Csaba. Their inspiring lectures as well as exercise sessions on different simulation and programming softwares were a golden opportunity for us to expand our skillset and knowledge sphere related to computing devices. Furthermore, the poster presentation, journal club session, panel discussion with all the speakers as well as plenty of individual interesting conversations with participants and speakers have definitely broadened our horizons regarding the emergent topic of spin based unconventional computing and we hope to draw benefits from this during our future research.

I was especially happy to reunite with my fellow SPEAR ESRs Maha and Ismael, with whom I spent many hours in scientific and unscientific discussions and who highly contributed to the great atmosphere at the school! I can’t wait to meet you again in Belgium soon!

Next to the massive scientific gain, personally, I also highly appreciate the experience of having organized such an event for a whole week which required nearly a year of preparation time to consider all different aspects necessary to hold a summer school.

As such a task is barely possible for one or few PhD students, I would like thank here my fellow organizing committee members (EPFL: Shreyas Joglekar, Andrea Muchietto, Mohammad Hamdi; ETH/PSI: Laura van Schie, and Zhentao Liu) for the joint efforts during the last year! Also, all the guest speakers and participants deserve my gratitude for showing high commitment and dedication to this school and establishing a great atmosphere in which everyone was happy to learn more from anyone else. Lastly, many thanks to the Doctoral school of EPFL (EDOC) and ETH Zurich for giving us this great opportunity to organize the school and the supporting professors Dirk Grundler (EPFL) and Pietro Gambardella (ETHZ) for their advice and guidance! I am looking forward to more of such events in future!

Settling in in Zurich

It has been several months since I have moved to Zurich, Switzerland, and in spite of few recent rainy and foggy winter days, I feel very well at home. Multiple reasons account for this: First of all, from my first few days I sensed the warm and kind atmosphere among my fellow PhD students and the whole research group lead by Prof. Pietro Gambardella. Whatever problem or scientific question I may have and occur during daily life, everybody likes to help and discuss all sorts of issues. This welcoming attitude greatly simplified my settling down process and enabled me during the last months to get accustomed to the measurement techniques to investigate magnetic tunnel junctions.

However, there is more to Zurich and Switzerland than only work: During the summer I exploited several days to enjoy the mountainous landscape by hiking and cycling. The first picture shows tired me during sunset after hiking up to Schilthorn summit, canton Bern, Switzerland.

One time, I cycled the Alps from Bodensee, Germany to Lago di Como, Italy. The Splügen pass, canton Graubünden, Switzerland is where we overcame the highest chain of mountains and is shown in the second picture. This crossing gave me a better feeling for the slighter and bigger variations in Swiss mentalities and lifestyles in different cantons – not to mention the differing but all great tastes of Swiss cheese.

Needless to say, but Zurich as the largest Swiss city does offer a plethora of opportunities to enjoy free time by itself: Bathing in the river (Limmat), having a barbecue at Zurich lake or walking the nearby hills, to enumerate only few.

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