A transmission electron microscope image of an EuO nanoparticle. Image: University of Konstanz.
A transmission electron microscope image of an EuO nanoparticle. Image: University of Konstanz.

Ferromagnetic semiconductors have attracted increasing attention over the past decade, as their properties make them promising functional materials for use in the field of spin-based electronics (spintronics). In an interdisciplinary collaboration, researchers at the University of Konstanz in Germany have successfully developed a method for synthesizing nanoparticles of europium(II) oxide (EuO), a ferromagnetic semiconductor with extremely promising properties.

The researchers also demonstrated that the nanoparticles have magnetic properties due to their structure. They report their findings in a paper in Advanced Materials.

The collaboration was carried out within the framework of the University of Konstanz's Collaborative Research Centre (SFB). It involved three research groups at the University of Konstanz, led by Sebastian Polarz (inorganic chemistry), Mikhail Fonin (experimental physics) and Ulrich Nowak (theoretical physics), and the electron microscopy team of the Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden), Germany, headed by Axel Lubk.

"Without the cooperation of these research teams, we could not have achieved these results," says Bastian Trepka, lead author of the study and a member of Polarz's research team on functional inorganic materials, which synthesized the nanoparticles.

The properties of anisotropic and magnetic nanoparticles are at the center of this research project. Anisotropic means that the magnetic, optical or electronic properties of the nanoparticles are not identical for all spatial directions. This makes it possible to investigate not only the impressive properties of nano-structured materials, but also the additional properties caused by anisotropy.

Producing nanoparticles from ferromagnetic semiconductors such as europium(II) oxide constitutes a huge challenge, especially in anisotropic geometry. "The aim is to deepen our understanding so that we can modulate and access the properties of nano-systems on demand," explains lead author Trepka. Using their special method, the researchers succeeded in synthesizing high-quality and anisotropic EuO nanoparticles, whose properties they could then study.

Their synthesis method is based on a two-stage process. In the first stage, the researchers produce a hybrid material consisting of organic and inorganic components, which is already anisotropic. In the next stage, they treat this hybrid material with europium vapor, which chemically converts it to EuO.

In this experiment, the researchers created tubular nanoparticles, but other shapes are possible as well. "This method is interesting because it is not limited to tubular forms. It is also possible to produce rods," explains Trepka.

Furthermore, the researchers were able to demonstrate that the magnetic properties of EuO are actually related to its shape, or rather the anisotropy. Further treatment caused the tubular shapes to disappear, resulting in different properties. "The experimental physicists carried out measurements that confirmed the results that had been simulated by the theoretical physicists. This enabled us to develop ideas as to how the structure brings about this particular magnetic behaviour," says Trepka.

"What is really special about our process is the separation of structure control and chemical transformation," he adds. "We can obtain different shapes from the same material by influencing the shape through process control. This way we will always get the material to assume the shape we need."

According to Trepka, EuO is "an intelligent material with a variety of properties". Above all, it has a simple crystalline structure. "We can explain changes in properties with appeal to the crystalline structures, which are pre-determined."

This story is adapted from material from the University of Konstanz, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.