Christian – Johannes Gutenberg University
After living and studying in Groningen for five years, I thought it would be nice to carry out my Master’s project abroad. So I contacted a professor at the University of Groningen to ask about connections abroad. I preferred a German-speaking country so that I could practise my German more, and that’s how I eventually ended up at Johannes Gutenberg University (JGU) in Mainz. Mainz is a city on the River Rhine in Germany and has a population of just over 200,000, of whom around 30,000 are students.
I was given the opportunity to carry out my research project at the Kläui Laboratory under the supervision of Professor Mathias Kläui. This is a fairly large group of PhD students and postdocs from many different backgrounds and nationalities, making it a very internationally oriented group. It was instructive to learn about some of the intercultural differences between countries. As my studies and project were conducted entirely in English, I will do my best to use the correct Dutch physics terminology in relation to my project, but I apologise in advance if I make any mistakes in the terminology.
Spintronics
The research group focuses on spintronics, a field with applications in, amongst other things, sensor and data storage technologies. Electrons have a negative charge, a property that is utilised in almost all modern electronic devices. In spintronics, another intrinsic property of electrons is exploited, namely electron spin. The electron spin is important, for example, in ferromagnetic materials; ferromagnetic materials exhibit a collective alignment of spins.
A well-known and commercially utilised application is MRAM: Magnetoresistive Random Access Memory. This storage technology is based on two magnetic layers that can either have a parallel magnetic orientation or an antiparallel magnetic orientation. According to the Giant Magnetoresistance (GMR, Nobel Prize 2007) or the Tunnelling Magnetoresistance (TMR) effect, a parallel magnetic configuration has a lower electrical resistance than an antiparallel configuration. We can use these two different states for storing binary data: specifically, where one state (low resistance) corresponds to a zero and the other state (high resistance) corresponds to a one. To change the data, one of the magnetic layers must be altered, which was the core of my research project: how can the direction of magnetisation of a magnetic layer be controlled?
Spin-orbit torques
To take things a step further, in my project I investigated spin-orbit torques in heterostructures of heavy metals and ferromagnets. To put it simply: spin-orbit torques are exerted by the heavy-metal layer (via the spin Hall effect), which exerts a torque on the magnetisation of the magnetic layer. This allows the magnetic orientation of the magnetic layer to be controlled and altered.
My research essentially consisted of three steps: fabrication, measurement and data analysis. First, I fabricated small ‘devices’ with thicknesses ranging from 2 to 30 nm and dimensions of 20 by 40 micrometres in the clean room, using sputtering and optical lithography. I then used various measurement set-ups to measure the effect of different thicknesses of both the heavy metal layer and the magnetic layer on the torques. During the data analysis phase, I processed the data and we drew conclusions. We are now in the process of publishing a scientific paper in a journal, so watch this space!
The research group
Right, that’s it for the technical bit for now! I’d like to elaborate a little on my experiences and what I’ve learnt whilst working within the research group. I’d particularly like to thank Prof. Kläui – first and foremost, of course, for giving me this opportunity, but also for all the inspiring moments, both academically and professionally. I particularly enjoyed the fact that I was given a great deal of freedom to carry out my research; whenever I was curious, I could simply pop into the lab and take some measurements. In addition, there was plenty of scope for advice and support; there was a fortnightly meeting where I could share my findings and get help with interpreting the results. One advantage of a large research group like this is that there’s always someone available to lend a hand!
That said, things do work a bit differently in Germany when it comes to logistics. I came face to face with German bureaucracy straight away when I had to sign what felt like a dozen forms before I could start working in the lab. One thing that is better organised in Germany, though, is the cheap meals at the universities! You could buy a set meal there for under four euros – something the University of Groningen could learn a thing or two about, given that a sandwich there costs nine euros. Although I must admit the quality wasn’t always great, as a poor student I made do with it.
Activities outside university
Alongside my research work, I tried to learn as much as possible about Germany during my time there. To be honest, I had slightly underestimated how difficult it would be to master the German language; despite five years of German lessons, it proved a bit harder than I’d expected. Fortunately, the German lessons I was able to attend at the university and the weekly Sprachcafé helped me to practise the language. It was also my first time celebrating carnival, which is called ‘Fastnacht’ in Mainz. I also went skiing for the first time, at a resort not too far from Mainz.
Another highlight during my stay in Germany was taking part in the ‘Europa macht Schule’ programme, which promotes intercultural awareness within Europe in German schools. I took part in their ‘Schulungswochenende’ and carried out a project with a German class at the IGS Rockenhausen. The theme of the project was cycling in the Netherlands and how travelling to school differs between different countries. It was a great success and it was brilliant to see how enthusiastic the pupils were about the project.
I had a wonderful and educational time in Germany and would like to thank KIVI very much for their grant, which helped make this possible!
