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ARTICLES IN ADVANCED MATERIALS

Research into Hybrid Interfaces and Magnetic Phenomena by Physicists at TU Dortmund University

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Cover of the journal Advanced Materials. © Mira Sophie Arndt
The team led by Professor Mirko Cinchetti uses spectroscopic methods to study physical phenomena that occur at two dimensional electronic systems. For the cover of the current issue of the journal “Advanced Materials”, the group designed graphics that show the interface between iron and a single layer of oxygen.
The research group led by Professor Mirko Cinchetti from the Department of Physics at TU Dortmund University has succeeded in publishing two articles at once in the renowned scientific journal “Advanced Materials”. The team is studying magnetic phenomena on ultrashort time scales and uses light to manipulate the magnetic and electronic properties of new materials. Their research work forms the basis for numerous potential applications – from information technology to spintronics.

Understanding hybrid interfaces – through experiments and simulations

In the first paper, Professor Cinchetti and David Janas, doctoral candidate and first author, have investigated – together with an international team – how the bonding of foreign atoms or molecules influences the properties of magnetic metal surfaces. When a surface is completely covered with an arrangement of such bound species, the result is an interface with uniform electronic and magnetic properties. Such hybrid interfaces play an important role in catalytic applications as well as in electronic and spintronic components. A better understanding of the physical phenomena and processes occurring at such interfaces can enable scientists to improve their performance for new technologies.

In their present work, the physicists from TU Dortmund University used spectroscopic methods to measure a high-purity iron film in ultra-high vacuum and examined the changes triggered by a single layer of oxygen atoms on the surface. The measurement technique they used is known as “spin-resolved momentum microscopy”, which makes it possible to capture the entire spin-resolved electronic structure of surfaces and interfaces.

The researchers supplemented their experimental results with theoretical simulations that show how the electrons in the metal influence each other. This mutual influence is also referred to as electron correlation. Including electron correlation in a simulation is complex and laborious in terms of computational effort, which is why it has so far been largely neglected. “With our work, we were able to show for the first time that adsorbates, that is, the particles bonded to the surface, can significantly increase the correlation effects between the electrons of a metal surface. In our case, this produces a completely new class of material with characteristics that can be attributed neither to metallic iron nor to insulating iron oxides”, says David Janas.

The team’s discovery might ring in a paradigm shift because it shows that electron correlation is not simply an abstract theoretical factor but instead important for understanding interface phenomena – and facilitates the design of innovative materials.

Cover of the journal Advanced Materials. © Mira Sophie Arndt
The graphics for the physicists’ article can be seen on the cover of the current issue.

 Link to the Paper

Also involved on the part of TU Dortmund University are Dr. Stefano Ponzoni and Dr. Giovanni Zamborlini. The paper was produced within the EU project “INTERFAST”, together with scientists from Trinity College Dublin (Ireland), Forschungszentrum Jülich, the University of Belgrade (Serbia) and the University of Augsburg.

Ultrafast control of magnetic properties

In the second paper, Professor Cinchetti and Fabian Mertens, doctoral candidate and first author, have studied – together with an international team – a van der Waals antiferromagnetic semiconductor (FePS3). The semiconductor belongs to a group of magnetic materials that are promising for information technology and spintronic applications, above all thanks to their robustness, potential speed and possibilities for miniaturization. To be able to use the semiconductors in technical applications, however, it must be possible to control their magnetic properties.

This is the starting point for the research work conducted by the team from TU Dortmund University: Through the targeted optical excitation of an electronic d-d transition below what is known as the “band gap” of the semiconductor, the team was able to excite a high-frequency (3.2 THz) vibration mode (phonon) of the iron ions in the semiconductor, which is closely coupled with the magnetic order of the material. Excitation below the band gap prevents the generation of free electrons and heat. By additionally applying strong magnetic fields, it was possible to hybridize this vibrational mode with a magnon, that is, a magnetic spin wave – and thus trigger coherent magnetic excitation.

The researchers were also able to apply the experiment to exfoliated layers a few hundred nanometers in thickness, which lays the groundwork for manipulating magnetic materials of atomic thinness.

 Link to the Paper

Also involved on the part of TU Dortmund University are David Mönkenbüscher and Dr. Umut Parlak. The paper was produced within the Transregio 160 project of the German Research Foundation and the EU project “SINFONIA”, together with researchers from the University of Valencia (Spain), Johannes Kepler University Linz (Austria) and the University of Konstanz.

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