Precise data on tiny magnets – Mathias Claus has developed a sensor that can be used to analyze the magnetism of tiny magnet

For his prizewinning master’s project in Professor Martino Poggio’s group at the Department of Physics of the University of Basel, Mathias Claus developed a torsion rocker that can be used to study the magnetization of tiny magnets in precise detail. His project was so successful that he began a doctoral dissertation immediately after his master’s with a view to optimizing the sensor so that it can also be used to investigate new, extremely thin, two-dimensional magnetic materials.

Mathias Claus also wins the prize for the best master’s thesis in nanoscience at the University of Basel. He has developed a sensor that can be used to analyze the magnetism of tiny magnets. (Image: C. Möller, SNI)

Fixed at two ends
The magnetization of small magnets is often analyzed by using tiny cantilever probes to scan the sample. For his master’s thesis, Mathias Claus has now explored a promising new way of studying the magnetization of extremely small magnets using a torque sensor that is also known as a “torsion rocker.” This mini seesaw is attached to springs on the right and left, causing it to swing back and forth like a pendulum at a specific frequency.

“Now, if we place a small magnet on this torsion rocker and apply an external magnetic field, the oscillation frequency of the sensor changes. How the frequency changes depends primarily on the magnetization of the tiny magnet,” explains Mathias Claus. “The measured change in frequency allows us to draw conclusions about the magnetic properties of the magnet.”

In this work, the researchers are assisted by previous computer simulations, which can be used to calculate the vibrational frequency changes as a function of magnetization. “The more closely the simulations agree with the measurement results, the more accurate the image we obtain of the magnetization and the more meaningful our analyses become,” explains Mathias.

 

Also suitable for superconductors
The sensor system that Mathias developed and tested for his master’s thesis can also be used to describe superconductors more accurately. To do this, the researchers position the circular superconductor in question on the torsion rocker, induce an electrical current within it, and change the temperature in the system. When they reach the critical temperature — that is, the temperature at which the superconductor conducts electric current without resistance — there is a dramatic change in the flow of current and therefore also in the magnetic field. In turn, this change can be measured based on the change in the oscillation frequency of the torsion rocker.

“The most impressive part about Mathias’ work is that we started with an idea for the ideal magnetic torque sensor at the nanoscale. Over the course of his project, Mathias developed a state-of-the-art fabrication process and, after testing the sensor, showed that it actually outperforms some of the previously used sensors.”

Professor Martino Poggio, Department of Physics, University of Basel

To display the torsion rocker Mathias needs to use a microscope.

Ongoing research
Mathias finds this topic so fascinating that he is continuing his research into the special new type of sensor immediately after his master’s degree — albeit now as a PhD student at the SNI PhD School. His work is supervised by Professor Ilaria Zardo and Professor Martino Poggio from the Department of Physics of the University of Basel.

The researchers are confident that a torque sensor of this kind could achieve significantly greater sensitivity than conventional cantilever sensors. There is still a lot of work to do, however. “Right now, I’m working on improving the quality factor of my device,” says Mathias. “With this in mind, it’s important to shield the lattice vibrations (phonons) of the torsion rocker so that fewer phonons from outside can couple with the sensor. At the same time, it’s also important to minimize the loss of phonons, which we need for the measurements.”

Mathias will subsequently establish a standardized production process and attempt to use the new sensor to characterize the magnetic properties of extremely thin, two-dimensional heteromaterials.

Above all, Mathias’s research will contribute to basic scientific analyses of micro and nano magnets. The new two-dimensional heterostructures that he wants to study have numerous potential applications in electronics, sensors and computer technology.

For his doctoral thesis, Mathias is optimizing the sensor he developed in his master’s thesis. (Image: C. Möller, SNI)

A latecomer to the world of physics
With this topic, Mathias has stumbled across a task that he really enjoys. “It’s fascinating how new lithographic methods allow us to produce such tiny structures — it’s almost like art,” he says.

It was only while doing his bachelor’s degree in nanosciences that Mathias developed a fascination with nanofabrication and physics. When he began the nanoscience degree in 2015, he was interested above all in the interdisciplinary and biological aspects of the program. Gradually, however, Mathias started to sense that physics was also the driving force behind many achievements in biology and medicine — and so he tried doing a block course in physics, as he explains: “I did a block course with Professor Zumbühl at the Cryo Lab and realized that I could do it when I put my mind to it.”

It’s now clear that things turned out for the best. For Mathias, the decision to leave Eastern Switzerland for Basel many years ago and to embark upon a nanoscience degree was absolutely the right choice. As well as the fascinating interdisciplinary curriculum, he particularly enjoyed the close contact with other students and lecturers. “I felt comfortable here in Basel right from the outset, and I’m now delighted to be able to continue my research within a fantastic team and as a member of the SNI PhD School.”

Further information:

Research group Poggio
https://poggiolab.unibas.ch

Short video with Mathias and Vera:
https://youtu.be/DyoPupfgaMs