From The Kiel University [Christian-Albrechts-Universität zu Kiel] (DE) And The University of Hamburg [Universität Hamburg] (DE): “Magnetic nano mosaics”

From The Kiel University [Christian-Albrechts-Universität zu Kiel] (DE)

And

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The University of Hamburg [Universität Hamburg] (DE)

10.5.22

PD Dr. Kirsten von Bergmann
Institute for Nanostructure and Solid State Physics
University of Hamburg
040 / 42838-6295
kirsten.von.bergmann@physik.uni-hamburg.de

Professor Dr. Stefan Heinze
Institute of Theoretical Physics and Astrophysics
Kiel University
0431 / 880-4127
heinze@theo-physik.uni-kiel.de

Press Contact:
Julia Siekmann
Science Communication Officer
Research area Kiel Nano Surface and Interface Sciences
jsiekmann@uv.uni-kiel.de
+49 (0)431/880-4855

Physics team from the universities of Kiel and Hamburg discovers new class of magnetic lattices.

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The image shows the different orientation of atomic “bar magnets” of an iron film: In a magnetic mosaic lattice (above), they are oriented in groups either upwards (purple) or downwards (white). In the skyrmion lattice (below), on the other hand, they point in all directions. © André Kubetzka.

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A measurement using spin-polarised scanning tunnelling microscopy (SP-STM) makes the hexagonal arrangement in the magnetic mosaic lattice visible on the nanometre scale. Due to a twist of the mosaic lattice on the atomic lattice, two rotational domains appear which deviate from each other by about 13° (see markings and graphs on the right). © André Kubetzka.

For about ten years, magnetic skyrmions – particle-like, stable magnetic whirls that can form in certain materials and possess fascinating properties – have been a focus of research: electrically easily controlled and only a few nanometers in size, they are suitable for future applications in spin electronics, quantum computers or neuromorphic chips. These magnetic whirls were first found in regular lattices, so-called “skyrmion lattices”, and later individual skyrmions were also observed at the University of Hamburg. Researchers from Kiel University and the University of Hamburg have now discovered a new class of spontaneously occurring magnetic lattices. They are related to skyrmion lattices, but their “atomic bar magnets” on the nanometer scale are oriented differently. A fundamental understanding of how such complex spin structures form, how they are arranged and remain stable is also needed for future applications. The results are published in the current issue of Nature Communications [below].

Quantum mechanical interactions

Attaching magnets to a refrigerator or reading data from a hard drive is only possible because of a quantum mechanical exchange interaction between the atomic bar magnets on the microscopic scale. This interaction, discovered by Werner Heisenberg in 1926, explains not only the parallel alignment of atomic bar magnets in ferromagnets, but also the occurrence of other magnetic configurations, such as antiferromagnets. Today many other magnetic interactions are known, which has led to a variety of possible magnetic states and new research questions. This is also important for skyrmion lattices. Here the atomic bar magnets show in all spatial directions, which is only possible due to the competition of different interactions.

“In our measurements, we found a hexagonal arrangement of magnetic contrasts, and at first we thought that was also a skyrmion lattice. Only later did it become clear that it could be a nanoscale magnetic mosaic,” says PD Dr. Kirsten von Bergmann. With her team from the University of Hamburg, she experimentally studied thin metallic films of iron and rhodium using spin-polarized scanning tunneling microscopy. This allows magnetic structures to be imaged down to the atomic scale. The observed magnetic lattices occurred spontaneously as in a ferromagnet, i.e., without an applied magnetic field. “With a magnetic field, we can invert the mosaic lattices, because the opposing spins only partially compensate for each other,” explains Dr. André Kubetzka, also from the University of Hamburg.

Surprising: Magnetically different alignment

Based on these measurements, the group of Prof. Dr. Stefan Heinze (Kiel University) performed quantum mechanical calculations on the supercomputers of the North German High Performance Computing Network (HLRN). They show that in the investigated iron films the tilting of the atomic bar magnets in a lattice of magnetic vortices, i.e. in all spatial directions, is very unfavorable. Instead, a nearly parallel or antiparallel alignment of neighboring atomic bar magnets is favored.

“This result completely surprised us. A lattice of skyrmions was thus no longer an option to explain the experimental observations,” says Mara Gutzeit, doctoral researcher and first author of the study. The development of an atomistic spin model made clear that it must be a novel class of magnetic lattices, which the researchers called “mosaic lattices”. “We found out that these mosaic-like magnetic structures are caused by higher-order exchange terms, predicted only a few years ago,” says Dr. Soumyajyoti Haldar from the group of Kiel.

“The study impressively shows how diverse spin structures can be and that a close collaboration between experimentally and theoretically working research groups can be really helpful for their understanding. In this field a few more surprises can be expected in the future,” states Professor Stefan Heinze.

Science paper:
Nature Communications
See the science paper for instructive images.
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About spin electronics:

In addition to the charge of the electrons, spin electronics also uses their so-called spin. This electron spin is a quantum mechanical property and can be understood in simplified terms as the rotation of the electrons around their own axis. This is linked to a magnetic moment that leads to the formation of “atomic bar magnets” (atomic spins) in magnetic materials. They are suitable for processing and storing information. Through targeted electrical manipulation, it would be possible to create faster, more energy-saving and more powerful components for information technology.

See the full article here .

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Stem Education Coalition

The University of Hamburg [Universität Hamburg] (DE) is the largest institution for research and education in northern Germany. As one of the country’s largest universities, we offer a diverse range of degree programs and excellent research opportunities. The University boasts numerous interdisciplinary projects in a broad range of fields and an extensive partner network of leading regional, national, and international higher education and research institutions.
Sustainable science and scholarship

Universität Hamburg is committed to sustainability. All our faculties have taken great strides towards sustainability in both research and teaching.
Excellent research

As part of the Excellence Strategy of the Federal and State Governments, Universität Hamburg has been granted clusters of excellence for 4 core research areas: Advanced Imaging of Matter (photon and nanosciences), Climate, Climatic Change, and Society (CliCCS) (climate research), Understanding Written Artefacts (manuscript research) and Quantum Universe (mathematics, particle physics, astrophysics, and cosmology).

An equally important core research area is Infection Research, in which researchers investigate the structure, dynamics, and mechanisms of infection processes to promote the development of new treatment methods and therapies.
Outstanding variety: over 170 degree programs

Universität Hamburg offers approximately 170 degree programs within its eight faculties:

Faculty of Law
Faculty of Business, Economics and Social Sciences
Faculty of Medicine
Faculty of Education
Faculty of Mathematics, Informatics and Natural Sciences
Faculty of Psychology and Human Movement Science
Faculty of Business Administration (Hamburg Business School).

Universität Hamburg is also home to several museums and collections, such as the Zoological Museum, the Herbarium Hamburgense, the Geological-Paleontological Museum, the Loki Schmidt Garden, and the Hamburg Observatory.
History

Universität Hamburg was founded in 1919 by local citizens. Important founding figures include Senator Werner von Melle and the merchant Edmund Siemers. Nobel Prize winners such as the physicists Otto Stern, Wolfgang Pauli, and Isidor Rabi taught and researched at the University. Many other distinguished scholars, such as Ernst Cassirer, Erwin Panofsky, Aby Warburg, William Stern, Agathe Lasch, Magdalene Schoch, Emil Artin, Ralf Dahrendorf, and Carl Friedrich von Weizsäcker, also worked here.

The Kiel University [ Christian-Albrechts-Universität zu Kiel ] (DE) was founded back in 1665. It is Schleswig-Holstein’s oldest, largest and best-known university, with over 26,000 students and around 3,000 members of staff. It is also the only fully-fledged university in the state. Seven Nobel prize winners have worked here. The CAU has been successfully taking part in the Excellence Initiative since 2006. The Cluster of Excellence The Future Ocean, which was established in cooperation with the GEOMAR [Helmholtz-Zentrum für Ozeanforschung Kiel](DE) in 2006, is internationally recognized. The second Cluster of Excellence “Inflammation at Interfaces” deals with chronic inflammatory diseases. The Kiel Institute for the World Economy is also affiliated with Kiel University. The university has a great reputation for its focus on public international law. The oldest public international law institution in Germany and Europe – the Walther Schuecking Institute for International Law – is based in Kiel.

History

The University of Kiel was founded under the name Christiana Albertina on 5 October 1665 by Christian Albert, Duke of Holstein-Gottorp. The citizens of the city of Kiel were initially quite sceptical about the upcoming influx of students, thinking that these could be “quite a pest with their gluttony, heavy drinking and their questionable character” (German: mit Fressen, Sauffen und allerley leichtfertigem Wesen sehr ärgerlich seyn). But those in the city who envisioned economic advantages of a university in the city won, and Kiel thus became the northernmost university in the German Holy Roman Empire.

After 1773, when Kiel had come under Danish rule, the university began to thrive, and when Kiel became part of Prussia in the year 1867, the university grew rapidly in size. The university opened one of the first botanical gardens in Germany (now the Alter Botanischer Garten Kiel), and Martin Gropius designed many of the new buildings needed to teach the growing number of students.

The Christiana Albertina was one of the first German universities to obey the Gleichschaltung in 1933 and agreed to remove many professors and students from the school, for instance Ferdinand Tönnies or Felix Jacoby. During World War II, the University of Kiel suffered heavy damage, therefore it was later rebuilt at a different location with only a few of the older buildings housing the medical school.

In 2019, it was announced it has banned full-face coverings in classrooms, citing the need for open communication that includes facial expressions and gestures.

Faculties

Faculty of Theology
Faculty of Law
Faculty of Business, Economics and Social Sciences
Faculty of Medicine
Faculty of Arts and Humanities
Faculty of Mathematics and Natural Sciences
Faculty of Agricultural Science and Nutrition
Faculty of Engineering