Research

In our research, we use micromagnetic simulations, Monte Carlo simulations, as well as analytical modeling to predict how magnetic materials and nanostructures respond to external stimuli and to interpret experimental observations of complex magnetic states. Here are brief descriptions of selected research highlights.

Direct observation of magneto-mechanical coupling in Nickel

In this project, in a collaboration between scientists at the Forschungszentrum Jülich in Germany, Beijing University, and South China University, we investigated the relationship between magnetism and mechanics, specifically how tensile strain affects magnetic domains in a ferromagnetic material. Using off-axis electron holography, a cutting-edge imaging technique, we observed the changes in magnetic domains in a Ni thin plate as it was stretched. The strain caused the formation of new magnetic domains, which were perpendicular to the direction of the strain, like the ones shown above. This effect was reversible, meaning that the magnetic domains returned to their original state when the strain was removed. We believe that this new insight to this well-known phenomenon could lead to new applications in areas such as magnetic sensors and data storage.

This study demonstrates the potential to control magnetic properties in materials using mechanical strain, which opens up possibilities for developing new types of solutions.

Magnetic sensors: The ability to manipulate magnetic domains with strain could lead to highly sensitive strain sensors, useful in areas like structural health monitoring, robotics, and wearable electronics.
Data storage devices: Controlling magnetic domains with strain could enable the development of new, denser, and more efficient data storage technologies.
Energy harvesting: The magnetoelastic effect can be harnessed to create energy harvesting devices that convert mechanical energy into electrical energy.

Overall, this research provides a new avenue for engineering magnetic materials with tailored properties for various applications.

Read the full article in Nature Communications here

Discovery of a new metallic phase in an Fe-Ni meteorite

In this international and inter-disciplinary collaborative research, we discovered a previously unknown Fe-rich tetragonal FeNi nanophase within the metallic meteorite NWA 6259. This nanophase exists alongside Ni-poor and Ni-rich nanoprecipitates within a matrix of tetrataenite (a chemically ordered form of FeNi).

The implications of this discovery are significant for several reasons:

New Understanding of Celestial Metallurgy: The discovery challenges the established understanding of Fe-Ni phase diagrams in meteorites and suggests the possibility of other, previously unknown, nanoscale phases in these extraterrestrial materials.

Advanced Magnetic Materials: The antiferromagnetic character of the FeNi nanophase, combined with the ferromagnetic nature of the other nanoprecipitates, results in a complex magnetic state. This could potentially lead to the development of new types of sustainable, high-energy magnets.
Improved Interpretation of Meteorite History: This discovery suggests that the magnetic properties of meteorites might be more complex than previously thought and can provide new insights into the thermal history of the meteorite.

In general, this discovery could have a significant impact on our understanding of extraterrestrial materials and their magnetic properties.

Read the full article in ACS Nano Letters here

Ferromagnetic resonance of iron-oxide nanoparticles

In this project, we looked at how superparamagnetic iron oxide nanoparticles (tiny magnets) behave when grouped together. It's commonly thought that these nanoparticles act independently due to their small size and constant change of magnetic state. However, this research showed that even in this state, the nanoparticles' magnetic fields can influence each other significantly.

We used a technique called ferromagnetic resonance spectroscopy (FMR) to study the nanoparticles in suspension and after they were dried. By carefully analyzing the experimental data with our theoretical models, we found that the nanoparticles in suspension behave differently than dried ones, suggesting that their arrangement influences their magnetic properties. This in turn suggests that the interactions between the nanoparticles create an additional magnetic field, affecting the overall magnetic behavior of the group. This can be seen in the spectra here by comparing the shape of the curves in the top and bottom panel. Even though the difference might appear small, the internal magnetic fields we extracted by fitting the experiment with our model is significantly different.

This research provides new insights into the collective magnetic properties of superparamagnetic nanoparticles, and this is important because it can help develop new applications for nanoparticles in fields like drug delivery, medical imaging, and in novel cancer treatment methods.

Read the full article in the Journal of Applied Physics here